Edinburgh Rhododendron Monographs

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Introduction

The Royal Botanic Garden Edinburgh has a history of research into the genus Rhododendron stretching
back over 100 years. The legacy of this work is a herbarium that contains many type specimens, an amazing living collection and many publications covering the whole genus.
A large amount of the written work on Rhododendron was created just before the digital age and so is only
available on paper and spread across many separate publications.
An example of this is what could be called "The Edinburgh Rhododendron Monograph". It covers almost a thousand species and was published over 26 years in seven separate publications across two journals and a book. It is not available or indexed in a single form anywhere.

In 2011 I was awarded a Encyclopedia of Life Rubenstein Fellowship to extract the species descriptions from these publications and make them available within EOL. On completion of this work I had a database filled with information about rhododendrons and decided to make it available in an electronic form. This publication is the result of exporting the data from the database.

You can hide this introductory text by clicking on the [-] on the top right.

Finding and Filtering

All the species descriptions are contained in this single HTML page in alphabetical order. Once the page has loaded in your web browser you should be able to use the browser's search function to find species and characteristics.

In addition to searching there is a simple filtering mechanism which will hide all species apart from those that appear to have certain characteristics. You can show and hide the filter by clicking on the links on the right.

Scope of Material

What is presented here does not contain the full texts from the source publications and is not meant as a replacement for them. All keys are omitted. All subgeneric, section, subsection, group and series descriptions and comments are omitted. All notes on cultivation and horticultural value have been omitted. There are no images (maps, diagrams graphs). What remains are the species, subspecies and variety descriptions along with notes on distribution, habitat and nomenclature.

The reader is referred to the source publications for the full text on anything not contained here. Each species description is accompanied by a full citation to the appropriate source publication.

Note on Quality

This is not a 'proper' publication in that it has not been edited or proof read. The text is of varying quality and contains errors. The reader should be aware of this and is expected to interpret the text on this understanding.

A major source of errors is the quality of the Optical Character Recognition (OCR) of the text scanned in the originals. The two source publications from the "Notes from the Royal Botanic Garden Edinburgh" have been scanned at high quality and should have fewer errors than the publications from "Edinburgh Journal of Botany" that were scanned manually. The most recent publication, George Argent's book on vireyas, was kindly made available in electronic form and so has not been through the OCR process.

A second source of errors is the tagging of the original text into a set of uniform fields for all species. This was done partially automatically and partially by hand with the possibility of errors being introduced at both stages. Sometimes the format of the original treatment does not fit a standard pattern and has had to be adapted.

A third class of error is systemic. This publication is a flat list of species descriptions extracted from a hierarchical set of taxon descriptions with no attempt to reconcile the fact that some of the characteristics of the species may only have been mentioned in higher level taxa in the source publication.

A final major source of errors could be termed the "Rumsfeld Errors" - the unknown unknowns. There may be sources of error that are unknown at this time.

In summary: This data is published on the understanding it would be more useful if it were available with errors than not available at all.

Further Work

This publication is a snap shot taken at the end of a project. There are currently no resources available for further development of this particular work although curation and research on Rhododendron at the Royal Botanic Garden Edinburgh continues.

Notes

Material seen in Kunming from NE Yunnan differs from the type in having rufous-tomentose perulae but is otherwise a good match. Lo Shiueh of McLaren is assumed to be Luoxue in NE Yunnan though this is not certain.

Habitat: Terrestrial in mossy forest and open shrubberies, especially on ridges, occasionally as an epiphyte but always in well-illuminated situations. Occurring from 1830 to 3350m, common on Mt Kinabalu but subject to fluctuations in the size of the populations as it is a species which appears to be very adversely affected by droughts in El Niño years.

Distribution: Malaysia (Borneo), Sabah, Mt Kinabalu and one record from Mt Alab in the Crocker Range.

Altitude: 1830-3350m

Notes

The only natural hybrid recorded is with R. fallacinum, a solitary intermediate plant without flowers growing within the zone of overlap between these two species on Mt Kinabalu. It would be surprising if hybrids with R. lamrialianum did not also occur but these may be difficult to recognise without flowers. In cultivation this species appears difficult – most records of it growing successfully when checked have proved to be R. rugosum which although with superficially similar leaves has quite different dendroid scales. Of the many introductions to the Royal Botanic Garden Edinburgh just one has grown successfully, although very slowly. It flowered for the first time in 1997. Rhododendron acuminatum is quite distinct amongst section Malayovireya species. The orange to red, more or less hanging flowers are produced in a moderate-sized umbel, the leaves are long-petiolate and strongly rugose, the veins deeply impressed on the upper leaf surface and strongly protruding beneath. These vegetative characters are sufficient to separate this species from R. fallacinum which grows together with R. acuminatum in part of its range on Mt Kinabalu. The flowers of R. acuminatum are very sparsely covered (if not glabrous) with much smaller scales than R. fallacinum and the limp, slightly hanging disposition of the flowers in R. acuminatum is quite different. The flower buds are unusual in this section in often having occasional scales on the margins amongst the simple hairs. The variation in this character needs further observation.

Notes

The density of the glands on the leaves and petioles varies considerably; the most glandular forms have a leaf indumentum that has a matted appearance. There is however no justification for maintaining the essentially glandular R. adenophorum as distinct from the eglandular R. adenogynum as there is no clear dividing line between them.

Notes

R. adenopodum has been traditionally included in subsection Pontica but differs from the remaining species in its stipitate-glandular ovaries and in its shallowly lobed corolla. Furthermore, its distribution is more in line with the other species in subsection Argyrophylla than it is with those of subsection Pontica.

Notes

Allied to R. glischrum and its immediate allies, but clearly differentiated by its leaf shape, texture and size. R. adenosum occurs in an area to the east of the range of R. glischrum. The wild-collected material lacks flowers; the details of the corolla have therefore been taken from cultivated specimens.

Notes

First introduced into cultivation by Dr Willem Meijer who collected seed from the type locality which was distributed by the Rijksherbarium in 1957 and grown successfully at Kew, where it was figured in Curtis’s Botanical Magazine (Hunt 1974). It was also collected by Peter Valder in 1975 (see History chapter); progeny from his plants are now widely cultivated. This species is one of the easiest of the albovireyas and has most attractive deep bronze new foliage. The bright orange flowers can be disappointing when the plants are young, often being overtopped by new foliage, but as the plant matures the flowers become more prominent and often give a wonderful display of colour. Flowering appears to be irregular in cultivation, often with two good flowerings a year and sometimes the occasional odd branch flowering out of synchrony with the rest of the plant.

Notes

R. aganniphum was originally distinguished from R. glaucopeplum by its supposedly eglandular leaf indumentum. The type of the former does however have a few glands; R. glaucopeplum is therefore reduced to synonymy.

Five specimens from S Xizang, an area to the W of the main range of the species, are atypical in their stiff broad leaves (resembling R. clementinae) but the corollas are 5-lobed. The status of these plants-Ludlow, Sherriff & Elliot 12002; Ludlow & Sherriff 811, 1568, 1760; and Kingdon-Ward 11613-s uncertain.

Notes

Closely allied to R. leptopeplum and R. tanastylum but distinguished from both by the glandular style and the leaf shape. Two gatherings, McLaren L 49 & L 60, may be hybrids of this species. The leaf indumentum suggests R. agastum but the more acute leaves and almost glabrous styles do not.

Distribution: Indonesia, New Guinea (W), Mt Agathodaemontop in Hellwig Mts; Mts Hubrecht and Wichmann on the southern and near Lake Habbema on the northern side of the Orange Mts; Mt Amdutakin in the Hindenberg Range. Papua New Guinea, Telefomin, West Sepik District and W of Oksapmin.

Altitude: 2500-3450m

Notes

Named after the mountain from which it was first collected which in turn was named after the Greek god Agathodaimon, the good genius, to whom a cup of pure wine was drunk at the end of dinner.

An odd form was collected by Katik & Taho (NGF 37952) from Tukwabit village, Lae, Morobe District. This is much further east than all the other collections and from considerably lower altitude (1800m). It had remarkably short broad flowers c.60mm long and with a broad tube up to 10mm wide. The bracts were shortly hairy outside and this specimen would appear to be intermediate between this species and R. herzogii or possibly a hybrid. The differences between R. agathodaemonis and R. herzogii are not clearly established. Sleumer (1973) modified his view of the difference from his (1966) Flora Malesiana account in the light of observations on flower length made by Peter Stevens and then made the chief difference fruit size. On the basis of limited herbarium specimens especially of R. agathodaemonis there does seem to be a difference in the corolla tube shape which is used in this account, and bract shape may produce further good morphological differences. Further observations are needed to clarify the situation.

Notes

Hybrids between R. alabamense and R. canescens are known to occur in Harris Co., Early Co. and Clarke Co., Georgia; Tishomingo Co., Mississippi; and Leon Co., Florida. These plants generally possess glabrous bud scales, and pink corollas with a yellow blotch on the upper corolla lobe. See Appendix for citation of representative specimens of these hybrids.

The variation in flower colour from all white to tinged with pink has been suggested
to be a result of hybridization and subsequent introgression with R. canescens (Skinner,
1955,1961). In addition, the slightly pubescent bud scales of some individuals have also
been considered as evidence of widespread hybridization (Skinner, 1961). While hybrids
between R. alabamense mdR. canescens do occur (see below), pink-tinged corollas also
occur in otherwise all white populations of R. viscosum, R. atlanticum and R. arboresc
ens. Therefore the pink blush on an otherwise white corolla does not necessarily imply
the historical occurrence of hybridization with a pink-flowered species. Likewise, the
variation in pubescence on the floral bud scales does not always require the occurrence
of hybridization with R. canescens. Pubescent bud scales are found scattered throughout
the range ofR. alabamense and do not seem to be more common in the southern part of this
species'range as suggested by Skinner (1961).

This species is more common in north-central Alabama, especially in Winston, Cullman and Tuscaloosa counties, than in other parts of its range where it has arather discontinuous distribution. The yellow blotch on the upper corolla lobe distinguishes R. alabamense from the other white-flowered species in eastern North America. It is isolated from the sympatric R. viscosum and R. arbor esc ens by flowering time. Without flower colour R. alabamense is often difficult to distinguish from R. canescens. In general R. alabamense has much less unicellular pubescent corollas and the floral bud scales are glabrous or only slightly unicellular pubescent. In addition, these two species are often ecologically isolated as R. alabamense occurs in dry woods and R. canescens usually occurs in bottom-lands and along stream banks.

Chromosome number: 2n = 26 (Janaki-Ammal et al., 1950; Li, 1957)

Flowering primarily in April and May, but occasionally as early as March or as late as June.

Notes

Only known from the type specimen which is apparently part of a mixed gathering which includes elements that have affinities with R. sperabile. R. albertsenianum and the next species, R. euchroum, share a bistrate indumentum, a rare feature in subsection Neriiflora.

Habitat: Undershrub in upper montane forest and forming thickets in open places at and above the tree line and along stream banks

Altitude: 1200-2300m

Notes

An erect growing shrub often with trailing branches from the base of the plant. The white nodding cup-shaped flowers scattered along the leafy branches are distinctive, and resemble a prunus rather than a rhododendron. The flowers are borne on short lateral leafy branches along the main stems and also below the terminal cluster of leaves.

Notes

Latin – albo – white; rugosum – the name of another superficially similar Bornean Rhododendron species but differing in the white (or very pale) flower colour.

It is known only from the mountain on which it was originally collected.

Rhododendron alborugosum is a very distinct species. It was originally confused with R. rugosum no doubt because of a superficial resemblance in the rugose leaves, but that species has dendroid scales, and pendent, much darker pink flowers. It has also been determined in the past as R. suaveolens Sleumer, which has superficially similar flowers, but that species has smooth, much larger leaves, a corolla which is glabrous outside and a much larger umbel of 14–20 flowers.

Notes

Rhododendron albrechtii is a phylogenetically isolated species of equivocal
relationship. It is possibly most closely related to R. schlippenbachii, R.
quinquefolium and R. pentaphyllum, being weakly linked with these species in at least
some cladograms on the basis of its dimorphic stamens (present in R. schlippenbachii and
slightly developed in R. pentaphyllum) and possibly also the loss of fringed seeds (see
Cladistic Analysis). The species is here considered tentatively to be an isolated (and
possibly cladistically basal) member of sect. Sciadorhodion. This placement agrees with
that arrived at by M. Philipson (1980) on the basis of cotyledon characters. It is
noteworthy that occasional multicellular gland-headed hairs similar to those of R.
pentaphyllum, R. quinquefolium and R. schlippenbachii occur on R. albrechtii cotyledons
in a varying but small proportion of different seedling populations (M. Philipson, 1970,
1980). The presence of such hairs may be an additional synapo-morphy linking this
species with sect. Sciadorhodion. However, a cladistic relationship to R. vaseyi (of
sect. Rhodora) can be hypothesized due to the presence of acuminate leaf apices in both
species. The seeds of R. albrechtii have a small appendage (or tail) at each end, as do
those of both R. vaseyi and R. canadense (a probable symplesiomorphy) and, like these
species, the vegetative shoots (bearing alternate and not obviously 5-whorled leaves)
develop from axillary buds associated with foliage leaves of the previous season (other
likely symplesiomorphies). The phenetic closeness of R. albrechtii and R. vaseyi has
been noted by Sargent (1888), Gray (1879), Rehder (1921a), and Wood (1961). It is likely
that R. albrechtii diverged early in the evolutionary history of Rhododendron subgen.
Pentanthera, and since nearly all features of this species are plesiomorphic,
determining the species'cladistic relationships are difficult.

Notes

Latin – alte – high up; cola – dweller. Alluding to the high altitude at which it was found.

Van Royen & Kores (1982) regarded R. alticola as a widespread and polymorphic species, transferring it to series Javanica (of Sleumer 1966) as the leaves of many collections exceed 40mm in length. It is certainly very similar to R. culminicola and differs from that variable species in that the ovary is said always to be without hairs. Material in Edinburgh has been cultivated under this name since 1967; this was collected by Michael Black (no. 81) from the Fatima River area and agrees with the informal description in van Royen & Kores (1982) of the form from that area, except that it has hairs on the inside of the corolla tube. Hairs inside the corolla have also been found on specimens from Mt Yule and the Bulldog Road – these may represent a different taxon. A Woods specimen (3064A) from the Mt Albert Edward area has sparse hairs on the ovary also and may represent a hybrid. The hybrid R. alticola x R. spondylophyllum was collected by Paul Kores from Mt Victoria and it would be surprising if hybrids with R. culminicola did not occur. High altitude species tend to be the most difficult to cultivate. The ‘Black’ collection grows well, with beautiful deep red flowers which are for some time held semi-erect due to the persistence of the bracts at the base in a collarette.

Rhododendron alutaceum var. alutaceum

Notes

Closely resembling R. taliense but with at least a few papillae or ramiform hairs on the ovary. The type specimen is apparently a mixed gathering; part is referable to var. alutaceum and part to var. russotinctum.

Notes

Closely allied to R. sanctum and possibly conspecific; differing in its often longer pedicels and in its red flowers. R. amagianum apparently flowers in mid July, about one month later than R. sanctum, and has an extremely restricted range.

Notes

The type of R. annae does have smaller flowers than is usual for the species and this has been used as the main diagnostic feature to separate R. annae from R. laxiflorum. The holotype of R. hardingii has equally small flowers however, while the isotype material has larger flowers and matches the type of R. laxiflorum.

Bodinier's type of R. annae is supposed to have been collected in Guizhou near Guiyang. If this is confirmed, then this species has a surprisingly disjunct distribution; all the remaining material comes from Mid-West Yunnan.

Notes

R. anthosphaerum is a variable species, both in leaf shape, and in corolla size and colour.
Several entities may be recognised within the species but complete intergradation apparently
occurs. The names used below are given only as a guide without implying any format taxonomic
status. 1. Leaves elliptic, apex ± acute..................R. anthosphaerum sensu stricto 4-
Leaves oblong to obovate, apex rounded and apicuiate....................-... .2 2. Leaves up to
8cm long............................................R. gymnogynum + Leaves 8-16cm
long.................................................................3 3. Corollac.30mm,
blue-magenta...................................R. chawchiense + Corolla 35 -45mm, crimson to
rose-magenta .,....................R. eritimum I am uncertain as to how far the four entities are
differentiated geographically, a problem that can only be resolved by detailed population
sampling. It is clear however that plants matching the types of both R. eritimum and R.
anthosphaerum occur together on the Sungkwei Pass and in the Lichiang Snow Range. However, plants
matching the type of R. eritimum appear to be more frequent in the northern part of the species'range.

Notes

Named after Mt Api, the mountain where it was found, which in the Malaysian language means ‘mountain of fire’. This is the only known locality of this species, which in addition has fiery-coloured flowers.

Rhododendron apiense is a peculiar species somewhat reminiscent of R. intranervatum Sleumer (from southern Sarawak) in having broad, sulcate leaves but it has sub-densely scaly (and minutely hairy), not laxly scaly young twigs, the ovary is only sparsely patently hairy, compared with the densely appressed hairy ovary of R. intranervatum, and it is much less sulcate. The mid-vein is only slightly raised beneath in this species, being level with the surface from about the midpoint of the leaf, often from the base, whereas in R. intranervatum it is strongly raised underneath to the apex. It differs from R. javanicum ssp. brookeanum, to which it is probably most closely related, in that the leaves are less than twice as long as wide with most leaves having a cordate base. It has distinctly basally apiculate anthers and a broader ovary with a shorter broader fruit. Apart from the distinctive leaf shape, the flowers differ from R. javanicum ssp. brookeanum in having larger, much more overlapping lobes and it grows at higher altitude than most forms of this species. Introduced into cultivation in Edinburgh in 1978, it is a lanky shrub which did not flower well until it was quite large and even then it has not produced the truly magnificent flowers which it did in the wild. It is still an attract­ive species and it is possible that it may perform better in climates with stronger light.

Flags

Rhododendron apoanum Stein

Erect shrub to c.1m, commonly branching from the base and branching profusely above as well. Twigs rounded, densely covered with dark-brown scales but these becoming paler and giving the stems a grey appearance with age. Leaves 3–6 together in loose pseudo­whorls, 2–7cm apart. Blade 30–110 x 10–40mm, elliptic to obovate-elliptic, variable in shape and size; apex shortly acuminate, sub-acute or obtuse; margin flat or slightly revolute, often irregularly somewhat crenate or dentate in the distal part; base broadly to narrowly tapering, dull silvery-green above often with a somewhat bluish tinge from a distance, initially densely scaly on both sides, those above predominantly silvery but with visible brown centres to the largest scales, glabrescent with age; below, densely and persistently brown-scaly, but often with narrow areas of the leaf surface visible between the scales. Scales with broad striate flanges and large swollen centres, the largest scales well spaced, with large dark centres. Mid-vein slightly impressed above, very prominent beneath in the lower part of the lamina; lateral veins 6–7 per side, irregularly spreading, the upper ones straight, all anastomosing, very slightly depressed above in fully mature leaves, somewhat raised or only faintly visible beneath, reticulation hardly visible. Petiole 9–15 x 2–3mm, weakly grooved distally, densely brown-scaly. Flower buds to 17 x 12mm, ovate, broadly pointed, with all bracts firmly appressed, purple or green. Bracts ovate to sub-circular, glabrous except for the fringe of simple white hairs and a patch of overlapping brown scales on the outside near the apex, which often extend down the middle line. Flowers 6–15 in an open umbel. Bracteoles filiform, shortly patently hairy and with a few scales especially towards the apex. Pedicels 7–11 x c.1mm, densely scaly. Calyx c.2mm in diameter, disc-shaped, covered in brown scales. Corolla 16–20 x 16–20mm, pinkish-orange; tube 13–18 x 4–7 x 5–9mm, straight, often somewhat 5-angled, glabrous or very laxly scaly outside, at least at the sinuses of the lobes; lobes 4–7 x 5–11mm, spreading horizontally or sometimes a little reflexed, broadly rounded or emarginate. Stamens at first clustered in the centre of the flower later spreading irregularly round and reaching or slightly exceeding the mouth of the tube; filaments linear, flat, glabrous; anthers broadly oblong, c.1.7mm. Disc green, glabrous or with a few scales on the upper side. Ovary 4–5 x c.2mm, sub-ovoid-conical, densely scaly; style as long as or shorter than the ovary, thick, scaly at the base, glabrous in the upper ½; stigma thick, rounded. Fruit 20–25 x 3–4mm, spindle-shaped. Seeds 5–6mm, without tails 0.8–0.9mm, the longest tail 3mm.

Notes

Named after Mt Apo where it was first collected, the highest mountain in the Philippines.

Copeland (1929) discusses the existence of two forms which had been suggested by Elmer (1911), one having slightly larger, entire, spreading leaves, the other with smaller leaves, ‘feebly dentate towards the apex, and tend[ing] to ascend strictly’. He concludes ‘that not even a varietal distinction can be made’ as the flowers are identical. In cultivation in Edinburgh there are two forms with differently coloured flower buds – purple and green – but with no other visible difference. This species might be regarded as an extreme variant of the R. malayanum complex but it is distinct in the smaller flowers which have a regular, circular or slightly 5-sided tube, not the laterally compressed tube characteristic of R. malayanum, as well as a shorter style. It is distinct from the only other Malayo­vireya so far known from the Philippines – R. nortoniae – by the much shorter flowers which are only ½ as long as in that species. Rhododendron apoanum was described and figured in the Gartenflora (Stein 1885) but the colour plate would appear to have been painted from a herbarium collection with directions from the collector as to the colours; there is no indication that it was cultivated. It took over 100 years to realise the horticultural promise of this species when it was finally introduced to cultivation via Edinburgh in 1993 from material collected on Mt Apo. It is one of the easiest species of this section to grow and flowers freely several times a year, the small size of the flowers being made up for by the freedom with which they are produced and the very attractive bluish-green aspect of the foliage.

Distribution: USA: West Virginia to Tennessee, North Carolina, Georgia and adjacent Alabama.

Altitude: 300-1500m

Illustrations:

Alexander, 1935

Prince, 1978 (photo)

Galle, 1985 (photo).

Notes

Rhododendron arborescens also hybridizes with R. cumberlandense and hybrids have been collected especially on Gregory Bald, Blount Co., Tennessee and in Jackson Co., Alabama. These hybrids vary considerably in morphology, from glabrous, white-flowered plants with unicellular-clliate bud-scale margins to pubescent, pink or reddish-flowered plants with glandular bud-scale margins. Putative hybrids also occur between R. arborescens and R. cumberlandense In Morgan County, Tennessee and in Union and Walker Counties, Georgia. Possible hybrids between R. arborescens, R. viscosum and J?, cumberlandense occur on Gregory Bald, Blount Co., Tennessee.

Rhododendron arborescens is most closely related to R. viscosum, and can be distinguished from It by the glabrous, yellow-brown branchlets, the red style and filaments which contrast with the white corolla and the distinctive seeds that lack a loose, expanded testa. Rhododendron arborescens is sympatric with R. viscosum and blooms during the same time of year. Both species are often found growing In close proximity to each other and hybridize occasionally, although these hybrids are sometimes difficult to detect. Reproductive Isolation may be related to pollinators as the fragrance of the two species is quite different and the flowers of R. viscosum have concolorous styles and filaments.

Chromosome number: 2n = 26 (JanaM-Ammal et al., 1950; Li, 1957)

Flowering from May to August, occasionally as early as April or as late as September.

Rhododendron arborescens is quite uniform morphologically throughout its range. The most noticeable variation occurs In leaf size and glaucousness which appear to be a function of habitat. Rehder (1921) described one form as a variety (R. arborescens var. richardsonii) which Is a smaU-leaved, compact form found In exposed situations on the tops of balds or mountains In the Appalachians.

Notes

R. arboreum is an extremely variable species, especially with respect to leaf shape and leaf indumentum, with a wide geographical range and clear-cut geographical differentiation. This species reaches its greatest complexity in NE India and adjacent E Nepal and Bhutan where there is intergradation between subsp. arboreum and subsp. cinnamomeum, though the former predominates below 2500m and the latter above 2900m. Subsp. delavayi apparently intergrades with subsp. arboreum in NW Burma where a range of intermediates occurs. It is also sometimes difficult to distinguish some forms of subsp. delavayi from subsp. cinnamomeum, especially where the ranges of the two approach one another, as in SE Bhutan. The two isolated subspecies, subsp. zeylanicum and subsp. nilagiricum, are closer to one another than they are to subsp. delavayi, from which they are clearly divided.

Notes

Latin – arenicola – sand dwelling, alluding to the fact that it was first collected on a dry sandy ridge.

Introduced into cultivation by Galloway and Smith from Mt Rantemario where it was common at 2700m. It flowered for the first time in cultivation in Edinburgh in December 2003 with most attractive pale pink flowers. Plants in cultivation tend to be less scaly than those from the wild, with dense but not overlapping scales on the undersides of the leaves.

Habitat: At the edge of forest,locally common, epiphytic or more rarely terrestrial.

Distribution: Indonesia, New Guinea (W), Arfak and Nettoti Mts.

Altitude: 1200-2135m

Notes

Named after the mountains from where this species was described.

Said to be close to R. angiense J.J.Sm. but differing in the shortly hairy pedicels and non-scaly corolla. Introduced into cultivation from seed sent by Professor Sleumer to the Australian Rhododendron Society in 1962. Doubtfully still in cultivation.

Notes

The corolla varies from open-campanulate (var. cupulare) to funnel-campanulate (R. argyrophyllum sensu stricto). This character, however, is lost in the herbarium and there is in any case considerable overlap.

Notes

A very imperfectly known species very similar to R. vaccinioides, differing chiefly in the pseudowhorled arrangement of the leaves. The isotype in Edinburgh is mixed with R. insculptum, and the paratype 7163 (also in Edinburgh) shows some variation in that it has faint pinnate venation which is not evident in the type, but this specimen is without flowers. This species apparently grows with R. insculptum but besides having differently coloured flowers is said to flower about one month later. It also differs in the smaller leaves without the very distinct lateral veins of R. insculptum and lacks simple hairs on the ovary.

Habitat: Terrestrial in heath-forest on ridges at the edge of degraded Nothofagus forest, or on the burnt open summit areas, on poor clayey soil, granite and quartzite

Distribution: Indonesia, New Guinea (W), Arfak Mts.

Altitude: 2150-2750m

Notes

Latin – asper – rough, alluding to the leaves which are rough due to the persistent epidermal tubercles.

Sleumer (1966) described wild hybrids of this species with R. laetum. These hybrids were characterised by glossy, shortly acuminate leaves, less distinct epidermal tubercles, the bracts densely hairy outside and c.2.5cm long. The pedicels were also scaly and hairy, the anthers c.4mm long, the ovary densely hairy and the corolla varying from pale greenish-yellow to pink and then often with yellow or greenish colour in the lower part of the tube.

Notes

Most probably allied to R. calophytum with which it shares the discoid stigma and large number of stamens but from which it differs in its stellate leaf indumentum, a unique feature in subsection Fortunea.

Habitat: Sandy pinelands, swamps, shrub bogs, or along streams. Femald (1942) cites this
species as 'thoroughly distinctive'of the Coastal Plain.

Distribution: Delaware to south-eastern Georgia along the Atlantic Coastal Plain

Altitude: 0-150m

Illustrations:

Ashe, 1921 (photo)

Harkness, 1932

Galle, 1985 (photo)

Notes

Chromosome number: 2n = 26 (Janakl-Ammal et al., 1950; Li, 1957)

Flowering primarily in April and May; however, this species may flower as early as March and Intermittently flower as late as November In the southern part of its range.

The relationship of Rhododendron atlanticum to the other white-flowered unblotched species, R. viscosum and R. arborescens, is not resolvable at present (see Phylogenetic Analysis). It Is distinct from both of these species by its flowering before or as the leaves expand. While!?, atlanticum Is isolated geographically from R. arborescens, it Is entirely sympatric with R. viscosum and is very similar to it morphologically. Rhododendron atlanticum Is quite variable In pubescence, flower colour and leaf size. Generally, however, It is more glabrous than R. viscosum, and has smaller leaves, which usually differ In length-to-width ratio from those of R. viscosum. In Virginia the leaves of R. atlanticum tend to be larger than the leaves of individuals throughout the rest of the species9 geographic range. Flower colour in R. atlanticum varies from white to pink (Weatherby & Griscom, 1934; personal observation) to white with a yellowish tinge (Femald, 1941). These forms have been formally recognized by Femald (1941) and by Ashe (1921) and Coker (1920), but in this treatment are not recognized because variation in corolla colour shows no correlation with other morphological characters or geographical distribution. Usually R. atlanticum is a low-growing, strongly rhizomatous species that has less well-developed branching than R. viscosum (which often can also be rhizomatous). However, sterile specimens of rhizomatous R. atlanticum and of glabrous, rhizomatous forms of R. viscosum can be nearly indistinguishable because of the natural variation within populations of R. atlanticum and R. viscosum.

Rhododendron augustinii subsp. augustinii

Leaves ± evergreen; corolla blue to purple with greenish or brownish spots. Petiole with filiform-acicular hairs only, or glabrous; corolla blue to lavender. Indumentum of leaf midrib beneath extending along the underside of the petiole; leaf upper surface with filiform-acicular hairs along most of the veins; corolla tube lepidote

Habitat: Rocky exposed sites and forest margins

Distribution: China (E Sichuan, Hubei, scattered)

Altitude: 1300-3000m

Illustrations:

Gard. Chron. 52:4 (1912)

Millais, Rhododendrons, opp. p. 24 (1917)

Urquhart, The Rhododendron 1: t. 6 (1958)

Notes

A distinct subspecies which vicariates with the more westerly subsp. chasmanthum; intermediates between the two occur in central and western Sichuan. R. vilmorinianum, on the basis of the type specimens, is clearly synonymous with subsp. augustinii; the description of vilmorinianum given by Balfour, and material identified as such by him and subsequent authors (Hutchinson, Davidian) is, however, a different plant which is known only in cultivation and is almost certainly a garden hybrid between R. augustinii and R. yunnanense. It has petioles and leaves fringed with loriform setae, the upper surface pubescent along the main veins and midrib, and a lepidote corolla tube; the leaf scales are like augustinii, but the characteristic patch of hairs on the midrib is lacking and the corolla is white or pink.

Rhododendron augustinii subsp. chasmanthum (Diels) Cullen

Leaves ± evergreen; corolla blue to purple with greenish or brownish spots. Petiole with filiform-acicular hairs only, or glabrous; corolla blue to lavender. Indumentum only on leaf midrib beneath, not or scarcely extending on to petiole; leaf upper surface glabrous or with filiform-acicular hairs along the midrib only; corolla tube elepidote, usually pilose outside.

Habitat: Forests, forest margins and scrub

Distribution: China (N & NW Yunnan, SW & NW Sichuan, SE Xizang)

Altitude: 2200-3650m

Illustrations:

Bot. Mag. 166: t. 79 (1949)

Notes

As mentioned above, subsp. chasmanthum vicariates with subsp. augustinii. The type of R. hirsuticostatum is somewhat intermediate between the two, but closer to subsp. chasmanthum than to subsp. augustinii

Rhododendron augustinii subsp. rubrum (Davidian) Cullen

Leaves ± evergreen; corolla blue to purple with greenish or brownish spots. Petiole with loriform as well as filiform-acicular hairs; corolla purple.

Habitat: Scrub and thickets,

Distribution: China (NW Yunnan)

Altitude: Around 4000m

Notes

A curious plant, known only from two gatherings and material in cultivation, in some respects (presence of loriform hairs, purple corolla) similar to R. trichanthum (p. 74). It is perhaps a naturally occurring hybrid, but field observations on this point are necessary.

Notes

The flower buds are very distinctive in this species, with short reflexed tips which are scaly both inside and out.

Rhododendron aurigeranum subsp. hirsutum Argent

Differing from the type subspecies by having both white hairs and scales on the outside of the corolla tube.

Habitat: It was growing at c.1520m in grassland above lower montane forest and appears to be well established as two collections were made 12 years apart from similar localities.

Altitude: Around 1520m

Notes

Latin – hirsutus – covered with long stiff hairs, alluding to the hairs on the outside of the corolla.

The flowers are described as yellow in one collection but with a yellow tube and salmon pink lobes in the other. Remaining colour in one of the herbarium sheets clearly indicates a yellow tube and pink or orange lobes.

Nomenclature

Rhododendron auritum Tagg

Very similar to R. xanthostephanum, differing as follows: often taller, bark not as conspicuous, leaves narrowly elliptic to elliptic, undersurface brown with unequal, ± contiguous or overlapping scales, the smaller sunk in pits but reaching the leaf surface; calyx lobes reflexed; corolla pale yellow or cream, sometimes with a faint pink flush.

Habitat: Sheltered cliffs

Distribution: China (SE Xizang—Tsangpo gorge)

Altitude: 2150-2600m

Notes

Very similar to R. xanthostephanum but consistently distinguishable by the reflexed calyx lobes and the less deeply sunk scales.

Notes

Rehder (1947) described a new form of R. roseum (= R. prinophyllum) from Stewartstown,
Pennsylvania, but the type specimen is indistinguishable from R. austrinum. Rehder
states that the plant grew in the woods near Gable's home in Stewartstown, although it is most likely an escape from cultivation.

Rhododendron austrinum is most closely related to R. luteum and R. occidentale. It is quite variable in flower colour, ranging from yellow to orange with a dark pink to red tube. Morphologically, it resembles R. canescens but can be distinguished from it by the consistently glandular nature of the bud-scale margins, pedicels, petioles and leaf margins. It is interesting to note that while the bud-scale margins of R. canescens can be mixed glandular and unicellular-ciliate in some populations, this character state is restricted to populations in central Georgia where R. austrinum does not occur. In areas where R. canescens is sympatric with R. austrinum the bud-scale margins of the former are consistently eglandular, as are the pedicels, petioles and leaf margins. These two species are usually isolated ecologically: R. canescens usually occurs in stream bottoms or low areas, and R. austrinum in upland woods. Hybrids do occur, however, and these usually appear intermediate in flower colour, but retain the eglandular nature of R. canescens. Specimens from Jackson Co., Mississippi are apparently R. austrinum, but those from neighbouring George Co. are entirely like R. canescens except for the orange-red flower colour noted on the label. Whether these specimens represent natural hybrids or whether they are cultivated hybrids is not possible to determine without further information.

Notes

Named after Carl G. Baenitz, German botanist and teacher.

Reported as being visited by a large butterfly by Tom Reeve in 1978. There is a letter in the Sydney Herbarium from T.L. Fenner, of the Department of Primary Industry, with the specimen, confirming the butterfly as Papilio euchenor.

Notes

There is no clear dividing line between var. balfourianum, with a compacted leaf indumentum, and var. aganniphoides, with a thick spongy indumentum; the two taxa are therefore not maintained as distinct. R. balfourianum resembles R. aganniphum in its foliage but the latter may be distinguished by its short calyx and glabrous ovary. The silvery leaf indumentum, sometimes turning pinkish, distinguishes the present species from the allied R. adenogynum.

Notes

Named after the collector, W.N. Bangham, an American who collected in Sumatra with his wife for the Arnold Arboretum.

Previously known only from the type collection, it was recently re-found and introduced into cultivation by Paul Smith from Mt Banda Hara in 2001. It is superficially similar to R. pubigermen but has much longer, more slender leaves as well as lacking hairs on the ovary. It has not been cultivated for long enough to know how it will perform as it only flowered for the first time in Edinburgh in 2005.

Notes

Closely allied to R. semnoides (q.v.). The following specimens are intermediate between R. basilicum and R. rex subsp. arizelum and are probably hybrids: Forrest 8990, 17691, 18116, 18375, 18860, 23284. These may be distinguished from R. basilicum by their only slightly flattened, scarcely winged petioles and by the strongly fimbriate cup-shaped hairs on the leaves.

Notes

Named after the famous Italian collector and early explorer Odoardo Beccari.

Apparently rare, not recently recollected and never cultivated. The status of this species is still very uncertain. The differences between this species and R. sessilifolium remain matters of degree. The orange or red flower colour suggests that this might be a hybrid between R. sessilifol­ium and perhaps R. rarilepidotum.

Rhododendron beyerinckianum Koord.

Slender, loosely branched, erect shrub or small tree to 5m. Twigs 1.5–4mm in diameter, thick to slender, densely to very densely covered with deep brown stellate scales which easily fall off and are absent from the older parts which are brown and rough with the numerous fine persistent tubercles; internodes 1.5–10cm. Leaves 3–7 together in pseudowhorls, often variable in shape and size in the same whorl. Blade 30–60 x 10–35mm, narrowly ovate, to broadly elliptic, obovate or sub-circular; apex obtuse, broadly acute, sometimes apiculate; margin strongly revolute to almost flat and more densely and often more persistently scaly than the rest of the leaf beneath; base broadly tapering or rounded; very densely reddish-brown scaly on both sides at first, quickly glabrescent especially above where it can become shiny but rough, more persistently scaly below. Scales irregularly stellately divided to the centre, dendroid, very fragile, each from the top of a minute, persistent, epidermal tubercle. Mid-vein slightly impressed above, strong and prominent beneath; lateral veins 4–7 per side, straight below, curved and anastomosing before the margin, very slightly impressed above and raised beneath, often inconspicuous or completely covered by the scales beneath, reticulation dense, visibly prominent on both sides in fully mature leaves, occasionally slightly impressed above. Petiole 4–15 x c.2mm, weakly grooved in the distal ½, or the groove inconspicuous, densely covered with brown stellate scales. Flower buds c.12 x 8mm, densely brown scaly with erect to slightly spreading bract points. Bracts to 10 x 7mm; the outer ones ovate subulate, densely scaly outside and fringed with marginal scales; the inner ones ovate acuminate and apiculate. Bracteoles to 10mm, linear and glabrous or scaly at first proximally, sub-­spathulate and laxly hairy distally. Inflorescence a 1–5-flowered open umbel. Flowers horizontal to half-hanging. Pedicels 10–15 x 7–10mm, densely brown-stellate scaly, becoming glabrescent. Calyx 3–4mm in diameter, disc-shaped or cup-shaped, densely stellate scaly or shallowly and obtusely 5-lobed. Corolla 20–45 x 10–18mm, most commonly dark red, at least at higher altitudes, sometimes pink or cream, rarely greenish or white; tube 15–25 x 4–7 x 6–10mm, curved or straight, at first densely covered with golden-brown stellate scales outside, completely glabrous inside; lobes 7–12 x 6–11mm, spreading perpendicularly, sub-circular, overlapping ½–2⁄3, scaly on the proximal part outside. Stamens unequal, clustered on the upper side of the mouth, slightly exserted to c.5mm; filaments linear, red, glabrous or rarely with a few hairs; anthers 2–2.5 x c.1.2mm, obovate-oblong, brown to dark red. Disc low, without simple hairs but sometimes with a few scales. Ovary 6–8 x 2.5–3mm, elongate-conical or sub-ovoid, densely stellate-scaly, usually abruptly tapering distally; style thick, as long as the stamens and exclusively stellate-scaly to the top at flowering, but becoming glabrescent distally as the fruit develops; stigma broadly obconical, slightly 5-lobed. Fruit 20–40 x 5–6mm, thick-fusiform, often a little wider in the distal ½, longitudinally grooved, densely brown scaly, usually with the persistent remains of the style. Seeds 2–4mm, without tails to 1.2mm, the longest tail c.1.5mm.

Habitat: Predominantly terrestrial but also epiphytic in mossy forest and on tree-ferns in grassland.

Distribution: Indonesia, New Guinea (W), along the Main Range from the Wissel Lakes. Papua New Guinea, main range east to Mt Vict­oria and Mt Dayman; also on Mt Saruwaged and Bismarck Mts.

Altitude: 1400-4000m

Notes

Named after M.W. Beyerinck, 1851–1931, a Dutch microbiologist.

A widely distributed species, both altitudinally and geographically. Sleumer (1966) conceived this species in a broad sense and acknowledged that it might ultimately be united with R. phaeochitum. For differences between this species and R. phaeochitum see under that species. Van Royen & Kores (1982) reported that it had been found on all major mountain ranges from the Nassau Mts to Mt Dayman and that ‘it is an extremely polymorphic species. Plants from different geographic locations vary considerably in stature, flower color, leaf size, leaf shape and texture. In addition the species also appears to vary throughout its altitudinal range’. Specimens of Rhododendron beyerinckianum obtained from lower altitudes tend to be larger, more robust than high altitude collections, their leaves are larger, less leathery and the indumentum is poorly to moderately well developed. Material from higher altitude tends to be more compacted than low altitude material, the leaves are smaller, more leathery, frequently somewhat revolute and the indumentum is generally very well developed’.

Notes

Only known from the poor isotype cited above. The leaves and glandular style suggest an affinity with R. cerasinum. There is also a (less likely) possibility that R. bonvalotii is a hybrid of R. souliei (subsection Campylocarpa); further material is required before a firm decision can be made.

Distribution: Indonesia, Kalimantan. Malaysia (Borneo), Sarawak and Sabah. Brunei. Widespread on the mountains of Borneo, said to be common on Mt Kemul, but only recorded in Sabah from Mt Lotung in the south.

Notes

Subsp. hypolepidotum is much more widespread than subsp. brachyanthum and much more variable, particularly in the density of the scales on the lower leaf surface. Some specimens have very abundant darker scales, whereas others have these very distant, though the yellow scales may be fairly close. In general, the closer the yellow scales, the more likely they are to have the milky appearance characteristic of those of R. pruniflorum.

Notes

Subsp. tigerstedii, from mainland Korea and the offshore Dagelet Island, is described as differing from subsp. brachycarpum in its larger leaves, 15-25cm long, and in its large white flowers (c. 70mm in diam.), etc. I have not seen sufficient wild-collected material of subsp. tigerstedtii to confirm the constancy of these differences, but from the description, the distinctions made appear to be relatively trivial.

Rhododendron brachycarpum subsp. fauriei (Franchet) Chamberlain

Leaves ± glabrous beneath when mature

Distribution: Japan, Korea

Illustrations:

Nakai, Fl. Sylva Koreana 8, t. (1919) - as R. brachycarpum

Notes

Ohwi (Fl. Japan, English Version, 698,1965) implies that R. brachycarpum of G. Don has entirely glabrous leaves and that R. fauriei is synonymous with it. However, Don clearly states that the leaves of R. brachycarpum have an indumentum on the lower surface. The synonymy cited here follows from the correction of this error. Nakai (loc. cit.) implies that all the material from Korea has glabrous leaves which is not entirely true. However, most of the Korean material seen is referable to subsp. fauriei which does appear to have a wider range than does the type subspecies. R. hidaense Makino (in Hara, Enum. PL Japon. 1: 33 (1948)-Type: Japan, Prov. Hida, in silva Aoya, vii 1939, Makino, n.v.) is probably a hybrid between this and the next species (see Hara, loc. cit.).

Notes

This species is based on a single specimen that has since been destroyed; Sleumer saw no material. The description here is modified from Sleumer’s translation of the original Latin. Copeland in discussing this species (1929) regarded it as related to R. teysmannii (R. javanicum ssp. teysmannii) and R. kochii. It would appear to belong to the R. javanicum complex but it is clearly distinct from R. kochii in both flower colour and leaf shape. Copeland also states: ‘On the other hand this species represents a transition from the ones just mentioned to R. leytense and R. loheri, which share the yellow flowers and appendaged anthers, but have somewhat smaller leaves, not at all acuminate, and drying to a dark brown colour. All the species here mentioned are alike in the hairiness of the ovary and filaments. Rhododendron brachygynum differs from all the others in the fact that the pistil is only about half as long as the stamens’.

The status of this species will not be satisfactorily evaluated without further collections from the type locality. It probably will turn out to be a minor variant of R. leytense (itself very similar to the R. javanicum complex). The very short pistil, the character to which Copeland appears to give most significance, may well be the result of examining very young flowers. The style elongates substantially in many species as flowers age and pass from the early unreceptive stigma phase to the later receptive one.

Notes

A distinctive species with extremely narrow flowers (amongst the New Guinea species of this group) reminiscent of R. jasminiflorum. The flowers were recorded in the field as becoming fragrant towards the evening.

Habitat: Shrubby forest, or grassy margins of Podocarpus forest, or open shrubberies on ridges, locally plentiful

Distribution: Indonesia, New Guinea (W), near Lake Habbema and the Wamena R. on N slope of Mt Wilhelmina (Trichora).

Altitude: 3200-3225m

Notes

Named in honour of Leonard Brass, famous for his botanical collecting expeditions in New Guinea.

Sleumer (1973) notes under R. ultimum that it may not be specifically different from that species. In fact, in the field, the differences are very obvious: R. brassii grows at a lower altitude and is a tall, erect shrub with green or silvery-green leaves, whereas R. ultimum is at higher altitude and is a low, spreading shrub with purplish leaves. Both have been grown side by side in cultivation and retain their distinctive habits. A hybrid with R. versteegii (R. x nebulicola) has been described from the wild by Danet (2005).

Distribution: Malaysia (Borneo), Sarawak, Mt Murud, Mt Lawi. Sabah, Mt Lotung, Crocker Range and in the area of the River Rekong Waterfall near Long Pasia. Erroneously reported from Kinabalu although it could easily be on that mountain.

Altitude: 1500-1600m

Notes

Named after B.L. Burtt, botanist at Edinburgh, who made a series of expeditions to Sarawak and who first collected this species with Adam Martin on Gunong Murud.

Habitat: In forest above 3100m, but more frequent in shrubberies and in open places amongst the granite rocks, up to 3900m.

Distribution: Malaysia (Borneo), Sabah, Mt Kinabalu.

Altitude: 3100-3900m

Notes

Latin – Buxus – Buxus sempervirens – ‘the European box’; folium – leaf. An allusion to the similarity of the leaves to that of this shrub.

The variety robustum recognised by Sleumer (1960) has little significance, except to indicate the effects of exposure: the type specimen is from the upper end of the range from an exposed site and thus has small leaves compared with the plants lower down. It is one of the most magnificent botanical sights on Mt Kinabalu when in full flower on a fine sunny day.

Notes

Like the ‘European box’ Buxus sempervirens, the leaves being superficially similar.

Flowers Apr, Oct.; probably continuously.

Sleumer (1973) commented that this species was ‘close to’ R. perakense but differed in the slightly crenulate leaves, red corolla and the bracts being both hairy and scaly outside. It is usually a much larger plant with bigger leaves and flowers. This species is not known to have been cultivated. In its small, dull red, densely scaly flowers it very much parallels R. inconspicuum and R. yelliotii from New Guinea. The almost tail-less seeds are like those of other species from the highest points on high mountains.

Habitat: Growing in the high open valleys dominated by tree-ferns and forming cushions on their trunks. Probably protected from frost and with optimal shading by growing usually about mid-way up the tree-fern trunks (Argent et al. 1999).

Habitat: Found in open, dry sites on southern and western exposures of hills and mountain-sides.

Distribution: USA: Northern West Virginia, south through the mountains of Virginia, North Carolina, Tennessee and Georgia. Generally restricted to the Ridge and Valley Province and Southern Appalachians, with occasional populations in the Cumberland Mountains and in the eastern edge of the Cumberland Plateau in Ohio and Kentucky. Not known west of die Tennessee River Valley in Tennessee. Extending into the Upper Piedmont in North and South Carolina and as far soutii as Meriwether Co., Georgia. Collections from Tarrytown, New York that are R. calendulaceum have been suggested as native in the past (Barnhart, 1895). However, all of the collections are nearly a century old and this is well north of the range of the species. Most likely these were cultivated plants that had persisted.

Altitude: 180-1000m

Illustrations:

Sims, 1815

Galle, 1985 (photo)

Notes

The morphological characters which are the most useful in distinguishing R. cumberlandense from R. calendulaceum are outlined in Table 6. These characters are most useful in the field. Identification can be made with much more confidence when a population is Investigated, as opposed to an isolated specimen. Individuals may be further identified by taking into consideration the geographic location and the altitude in combination with the height and habit of the plant. Rhododendron cumberlandense is primarily a plant of the higher elevations of the Cumberland Plateau and Mountains where it flowers well after the leaves have expanded (this is one of the most useful characters). It is usually of smaller stature and glaucous leaves are much more common in populations of R. cumberlandense than in R. calendulaceum. The results of this study show that R. calendulaceum is morphologically separable from R. cumberlandense when a combination of characters is used in conjunction with geographic location. These two species can be most easily identified in the field where populations can be examined for variability in pedicel indumentum and sepal margin condition, and where phenological conditions can be clearly discerned. It is still difficult to identify some individual specimens because the range of morphological variation in R. calendulaceum may occasionally obscure the differences between the two species. However, difficulty in identification is not necessarily a valid reason to consider R. cumberlandense as conspecific with R. calendulaceum (Willingham, 1973). Rhododendron calendulaceum was once thought to be the red-orange-flowered taxon in the hybrid swarm on Gregory Bald, Blount Co., Tennessee. However, Li (1957) showed that all individuals sampled from that locality were diploid, and thus the red-orange species is the diploid, R. cumberlandense. However, a few specimens from Gregory Bald are indistinguishable morphologically from R. calendulaceum, and this species Ukely occurs on the bald in small populations. Although of low probability, hybrids with the tetraploid are not impossible since unreduced gametes are fairly frequent in the Ericaceae (Li, 1957; Goldy & Lyrene, 1984). The putative hybrids listed in the Appendix exhibit a combination of characters that occur where R. cumberlandense is not known to occur, and with species whose blooming times overlap with that of R. calendulaceum, but not R. cumberlandense. As such, these plants are most likely the result of hybridization by unreduced gametes.

Several specimens previously classified as 'intermediates'fit best Into the natural range of variation of R. calendulaceum and are best classified as the tetraploid, based upon morphological Information. Rhododendron cumberlandense is less morphologically variable than R. calendulaceum, in that the pedicels and sepal margins are almost always eglandular, and only occasionally one or the other will be somewhat glandular. From the R. cumberlandense populations examined, the only individuals with both completely glandular pedicels and sepal margins occurred In Alabama, in a population of hybrids between R. arborescens and R. cumberlandense. By contrast, this character combination occurs frequently in R. calendulaceum. Field-work In Virginia and North Carolina confirms the generally eglandular nature of R. cumberlandense and the glandular nature of R. calendulaceum.

Principal component analysis of 39 OTUs and up to 40 floral, bud-scale and vegetative
characters were performed. Most of the characters were so variable that they only
resulted in adding a great amount of 'noise'to an akeady complex problem. Therefore a series of analyses was performed, and from these, six characters (see Table 5) were chosen for an additional analysis. These six characters consistently recurred In each of the previous analyses as characters which were heavily weighted In the first and second principal components. The results of this analysis, using 39 OTUs and six characters, are shown In Fig. 25. Some definite trends are evident. Using the character of flowering time (which was not used In the principal component analysis) tentative assignment of specimens to either R. cumberlandense or R. c(ilendulaceum was made. There Is a trend towards Increasing floral size from the diploids to the tetraploids. However, there is no morphological gap in corolla size. The variation In the Indumentum of the pedicels and In the sepal margins from eglandular to glandular Is an Important trend. In the R. cumberlandense specimens, the pedicels and sepal margins are usually both eglandular, while in most specimens of R. calendulaceum the pedicels and sepals are glandular. Leaf pubescence appears to be highly variable. There is only a weakly defined trend towards densely unicellular pubescent leaves in R. calendulaceum.

The tetraploid flame azalea, R. calendulaceum, has long been noted for its
morphological variation (Bartram, 1791; Rehder, 1921; Skinner, 1955, 1961; Galle, 1968,
1985). This species is found throughout the Blue Ridge and into the Ridge and Valley and
Piedmont provinces. The closely related R. cumberlandense is diploid and has a more
discontinuous occurrence within Its geographic range than the tetraplold, occurring
primarily In the Cumberland Plateau and Mountains. While these two taxa are distinct
biological entities, they are often very difficult to separate on the basis of
morphology. This Is due to the great range of morphological variation In R.
calendulaceum (WEEngham, 1973; personal observation) and also in part to the natural
variation found in populations of R. cumberlandense. The characters which have been used
to distinguish between these two species (besides chromosome number) include flavonoid
chemistry (King, 1977a, 1980), flowering time and leaf expansion (Lemmon, 1938; Braun,
1941; Skinner, 1955, 1961; Galle, 1968, 1985), size of the corolla (Braun, 1941;
Skinner, 1955, 1961; Galle, 1968, 1985), pubescence of the abaxial surface of the leaves
(Skinner, 1955, 1961; Galle, 1968, 1985), and habit (Braun, 1941; Skinner, 1955, 1961;
Galle, 1968, 1985). Rhododendron calendulaceum is characterized in the Eterature as tall
usually non-stoloniferous shrubs possessing flowers which open before or as the leaves
expand, and are up to 4cm across. In addition, R. calendulaceum is cited as possessing
unicellular pubescent abaxial leaf surfaces (Rehder, 1921; Braun, 1941; Skinner,
1955,1961; Galle 1968,1985). By contrast, R. cumberlandense has been described as a
low-growing stoloniferous shrub, with smaller, redder flowers, and more glabrous leaves
than R. calendulaceum(Bmw, 1941; Skinner, 1961). The primary difference which has been
emphasized in the literature has been the flowering of R. cumberlandense after the
leaves have fully expanded. Difficulties in identification arise because there are no
gaps in the flower size and colour or in leaf size or pubescence, and the phenologlcal
differences are sometimes difficult to discern from herbarium material. Both R.
cumberlandense and the 'early' and late'-blooming forms of R. calendulaceum have been studied in the Nantahala Mountains and nearby areas In North Carolina and Georgia by Willingham (1973,1974, 1975,1976). No morphological or phenological gaps were found between the early and late forms of R. calendulaceum. To distinguish between the two species WElingham used the following characters: growth habit, leaf expansion, flower colour, flower size, presence or absence of a blotch, pollen size (tetrad), pollen viability, cuticular ridging of the epidermis, stomata size and flavonoid compounds. Of these characters, only flavonoid compounds, pollen size and pollen viability were considered reliable characters in distinguishing between the two species by Willingham. He did note the difficulty in distinguishing the later-blooming individuals of R. calendulaceumfmm Individuals of R. cumberlandense, as late-blooming R. calendulaceum often has most of its leaves unfolded (however, there are usually some vegetative bud scales remaining on the plant). These late-blooming individuals almost always possess multicellular gland-tipped hairs on the pedicels and the sepal margins, whereas R. cumberlandense has eglandular pedicels and sepal margins. Earlier-blooming individuals of R. calendulaceum appear to be more variable in pedicel and sepal margin condition, with either the pedicel or sepal margins being eglandular. Plants of R. calendulaceum with both eglandular pedicels and sepal margins are usually clearly blooming before or with the expansion of the leaves. In Kentucky the pedicels and sepal margins of R. calendulaceum are more often eglandular than in West Virginia where they are usually glandular.

Notes

Latin – caligo – of mist or fog, the type collection being made from plants that seemed perpetually enshrouded in mist.

A striking species owing to its linear leaves which are densely covered with dark brown, dendroid scales when immature and its apparent association with limestone outcrops. Similar to R. hooglandii from which it is best distinguished by its subulate bracts which are densely scaly outside. For a discussion of other differences see under R. hooglandii.

Notes

Cowan & Davidian maintain R. myiagrum at specific rank while admitting that the only significant difference between it and R. callimorphum is the flower colour, a distinction that certainly does not merit more than varietal rank.

Notes

Very similar to subsp. riparium but differing in its larger leaves and flowers, and the scales on the leaf undersurface not being so clearly tiered, presenting a smooth, almost felted appearance. Restricted to the mountains around Weixi (Wei hsi), where R. saluenense subsp. chameunum also occurs. It may be a stabilised hybrid between R. calostrotum and subsp. chameunum.

Notes

A northerly vicariant of subsp. calostrotum, occupying quite a wide distribution area. The small-leaved variants, described as R. nitens and R. calciphilum are in many ways intermediate to subsp. keleticum.

Notes

Var. duseimatum may be a chance hybrid between R. selense and var. calvescens, especially since it has only been collected once and then from a well-known locality. R. calvescens is closely allied to R. dasycladoides, sharing with it the rufous dendroid-hairy ovary, but differing in the lack of bristles and in the more persistent leaf indumentum.

Rhododendron camelliiflorum Hooker

Shrub to 2 m, epiphytic or growing on rocks. Young growth lepidote. Leaves narrowly elliptic to oblong-elliptic, bluntly acute at the apex, tapering to a shortly rounded base, (53-)60-90(-105) x (16-)20-30(-37) mm, shining dark green above with few, dried-out scales, pale green to brownish beneath with a dense covering of almost contiguous, broadly rimmed scales of which a few are larger and darker than the rest. Inflorescence 1-2-flowered, pedicels densely lepidote. Calyx lobes oblong, rounded at the apex, 5-8 mm, lepidote or not on the surface, fringed with scales. Corolla waxy, with a short, broad tube, white to deep rose, rarely with a whitish or yellowish zone within at the base, lepidote outside, villous within, 14-18(-20) mm, tube 8-10 mm. Ovary 5-10-locular, lepidote, style usually shorter than the stamens. Capsule ovoid, lepidote, tapered to the apex, 7-11(-13) mm

Habitat: Forest and forest margins, cliffs

Distribution: Nepal, India (Sikkim), Bhutan

Altitude: 2750-3650m

Illustrations:

Bot. Mag. 82: t. 4932 (1856)

Gartenflora 14: t. 460 (1865)

Notes

R. lucidum Nuttall, Hooker's Kew Journ. 5: 363, 1853 (Type: On the mountains of Bootan (i.e. India, Arunachal Pradesh, cf, Ludlow, loc. cit.), beyond the Bhorelli, Booth—holo. K) is based on a plant without flowers or fruits. It is probable that it is merely a variant of R. camelliiflorum.

Rhododendron campanulatum subsp. aeruginosum (Hooker f.) Chamberlain

Leaves 7-9.5cm long (wild specimens), coriaceous, opening with a bluish metallic bloom on the upper surface; corolla lilac or purple.

Habitat: Alpine slopes

Distribution: N India (Sikkim), Bhutan, ? E Nepal

Altitude: 3800-4500m

Notes

All specimens seen of subsp. aeruginosum have small coriaceous leaves and in this respect agree well with the type specimen. However, the characteristic bloom on the upper surfaces of the leaves is usually lost on drying so it cannot be observed on most herbariaum material. I have not seen any specimens from C and E Sikkim or from Bhutan that match W Himalayan specimens in the size of their leaves but there is a series of fruiting specimens, presumed to have been collected in Sikkim (Cave 6719, 6726, 6983; Watt 5245, 5295, 5296), with leaves 7.5-9cm long, but subcoriaceous and with a less thick indumentum than is usual in subsp. aeruginosum. These may be considered as being intermediate between the two subspecies. There is also a series of intermediate plants in cultivation from E Nepal (Spring-Smythe 7, 8, 9, 11, 17, 41, 44). On present evidence therefore, subsp. aeruginosum apparently replaces subsp. campanulatum in the east but there is a zone of overlap.

Nomenclature

Rhododendron campylocarpum Hooker f.

Shrub or small tree, 1—4(—6.5)m; young shoots usually with a few short stipitate glands. Leaves orbicular to elliptic, 3.2-10 x 1.5-5cm, 1.1-2.5 x as long as broad, apex rounded and apiculate, base ± cordate, upper and lower surfaces glabrous when mature, rarely with a few glands at base below; petioles 0.5-2.2cm, stipitate-glandular, at least when young. Inflorescence 3 —10(—15)-flowered; rhachis 3-5mm, rarely up to 20mm; pedicels 10-35mm, stipitate-glandular. Calyx 3-5mm, stipitate-glandular, lobes rounded. Corolla campanulate, pale to sulphur yellow, sometimes tinged with red in bud, with or without a basal blotch, 25-40mm. Ovary densely stipitate-glandular; style glabrous or glandular for up to one third of its length. Capsule 13-20 x 4-7mm, curved.

Notes

Apparently intergrading with subsp. campylocarpum though probably entirely replacing it in the eastern part of the range of the species. Some forms of subsp. caloxanthum have a marked glaucous bloom on the lower surface of the leaves. These have been referred to R. telopeum. This character is difficult to see in dried material and there are plants from the western part of the range of subsp. campylocarpum that also have glaucous leaves. It therefore seems likely that they are no more than local habitat forms, perhaps showing a response to more exposed conditions. A specimen from SE Xizang, Ludlow, Sherriff & Elliot 13756, is a hybrid of R. campylocarpum, possibly with R. stewartianum as the other parent. R. campylocarpum also hybridises with R. wardii (q.v.) where the ranges of the two species overlap.

Notes

Several specimens from Fuchuan, SW of Weixi in NW Yunnan are technically referable to subsp. campylocarpum though they have leaves that are relatively small and which sometimes have rounded bases. These might be part of a stabilised hybrid population with subsp. caloxanthum and R. selense s.l. as putative parents, especially as this locality is outside the normal range of subsp. campylocarpum. These specimens are as follows: McLaren D 231; Rock 16980, 16996, 17011, 17012, 17019, 18353, 18373, 18393.

Rhododendron camtschaticum subsp. glandulosum (Small) Hulten

A lower growing plant with narrower corolla lobes. The leaves of the vegetative shoots are distinctly glandular-hairy and the outer surface of the corolla lobes is glabrous (or virtually so) and margins are not ciliate.

Notes

Over most of the range of the species these two subspecies are morphologically distinct and have separate geographical distributions, However, intermediate forms occur in the zone where the two subspecies meet (see Hulten, op. cit.).

Distribution: Distributed from Newfoundland and Quebec, south to eastern Pennsylvania and northern New Jersey.

Altitude: 0-1900m

Illustrations:

Meerburgh (1798)

Sims (1800)

Duhamel (1806)

Britton & Brown (1897)

Marie-Victorin (1947)

Graves (1956)

Gleason (1952)

Campbell & Hyland (1975)

Notes

Rhododendron canadense is a very distinctive species most closely related to R. vaseyi; see discussion following the latter species. Although originally described as the genus Rhodora (Linnaeus, 1762), its close relationship to Rhododendron has long been recognized (see Rehder, 1921a; Sleumer, 1949, 1980; Wood, 1961).

Rhododendron canescens (Michaux) Sweet

Shrub or small tree to 6m tall, usually non-rhizomatous; young twigs red-brown, sparsely to densely covered with unicellular hairs and multicellular eglandular hairs, occasionally with only unicellular hairs, or with unicellular hairs and multicellular gland-tipped hairs, rarely glabrous. Vegetative bud scales densely covered with unicellular hairs abaxially; margin unicellular-ciliate or glandular. Leaf blade membranaceous, ovate or obovate to elliptic, (4.7-)5.9-8.5(-9.8) x (1.4-)1.9-2.8(-3.6)cm; base acute to oblique; apex acute to obtuse, often mucronate; adaxial surface sparsely to densely covered with unicellular hairs, or also with multicellular eglandular hairs, occasionally only with multicellular eglandular hairs, rarely with unicellular hairs and multicellular gland-tipped hairs, the midvein densely covered with unicellular hairs; abaxial surface sparsely to densely covered with unicellular hairs, rarely also with multicellular eglandular hairs, or glabrous, the midvein densely covered with unicellular hairs and multicellular eglandular hairs, or rarely with multicellular gland-tipped hairs or only unicellular hairs; margin entire, rarely minutely serrulate, ciliate with multicellular eglandular hairs, rarely with a few multicellular gland-tipped hairs at the base of the blade; petiole (0. l-)0.2-0.4(-0.5)cm long, sparsely to densely covered with unicellular hairs and multicellular eglandular hairs, occasionally with unicellular hairs and multicellular gland-tipped hairs, rarely with only unicellular hairs. Flower bud scales chestnut brown; abaxial surface densely covered with unicellular hairs; margin unicellular-ciliate, occasionally with both unicellular hairs and glands. Flowers appearing before or with the leaves; inflorescence a shortened raceme of 6 to 19 flowers. Pedicels (0.4-)0.5-l .0(-l .3)cm long, sparsely to densely covered with unicellular hairs and multicellular eglandular hairs, occasionally with unicellular hairs and multicellular gland-tipped hairs, rarely with all three types of hairs. Sepals less than 0.1-0.2(-0.4)cm long, often varying in length on the same flower; margins setose, occasionally also with multicellular gland-tipped hairs, or only glandular-fimbriate; abaxial surface densely covered with unicellular hairs, or also with multicellular eglandular hairs, occasionally with unicellular hairs and multicellular gland-tipped hairs, rarely with all three types of hairs. Corolla pink, or the tube pale to deep pink and the lobes pale pink to white, occasionally white or rose to deep pink throughout, fragrance musky-sweet, the tube longer than the limb and gradually expanding into it; upper corolla lobe (0.7-)0.8-l .3(-l .5) x (0.6-)0.7-l .0(-l .4)cm wide; lateral lobes (0.8-)1.0-1.5(-2.0) x (0.3-)0.5-0.8(-1.0)cm; corolla tube (1.3-)1.5-2.0(-2.6) long, (0. l-)0.2-0.3(-0.4)cm wide at base; outer surface of corolla densely covered with unicellular hairs and sparsely to densely covered with multicellular gland-tipped hairs that occasionally continue up the corolla lobes; inner surface of corolla sparsely to densely covered with terete or rarely flattened unicellular hairs. Stamens (3.1-)4.4-5.7(-6.4)cm long, with dense terete or flattened unicellular hairs on proximal (0.0-)2.0-3.1(-4.1)cm of filament, exserted (1.7-)2.5-3.6(-4.5)cm beyond throat of corolla. Style (3.7-)4.4-5.7(-6.8)cm long, exserted (2.0-)2.7-3.9(-4.8)cm beyond throat of corolla, with dense unicellular hairs on proximal (0.0-)0.7-2.0(-3.3)cm; stigma 0. l-0.2cm wide. Ovary 0.3-0.4(-0.5)cm long, 0. l-0.2(-0.3)cm wide at the base, densely covered with unicellular hairs and multicellular eglandular hairs, occasionally also with multicellular gland-tipped hairs, or with unicellular hairs and multicellular gland-tipped hairs; the multicellular hairs may cover the unicellular hairs or may only occur on the ribs of the ovary; the nectary is crowned with a dense ring of unicellular hairs. Capsules (1.2ó)1.5ó2.1(ó2.5) x 0.3-0.5cm wide, narrowly ovate to cylindric, moderately to densely covered with unicellular hairs and sparsely to moderately covered with multicellular eglandular hairs. Seeds pale to dark chestnut brown, ovate or elliptic to fusiform, (1.2-) 1.6-2.5(-3.0) x (0.3-)0.5-0.8(-l.l)mm, body (0.6-)0.8-1.2(-1.4) x (0.1-)0.3-0.5(-0.6)mm; testa expanded and dorsiventrally flattened, surrounding the body, with both elongate and short cells scattered throughout the testa, the short eels more common in the expanded portion of the testa, with tapering end-walls

Habitat: River bottoms and stream banks, low flatwoods, dry clearings and open woods.

Distribution: Tennessee and southern North Carolina, south along the Coastal Plain and Piedmont to peninsular Florida, west to eastern Texas and Oklahoma, north to Union Co., Illinois (Fig. 27).

Altitude: 0-500m

Notes

Chromosome number: In = 26 (Janaki-Ammal et al., 1950; Li, 1957)

Flowering from March to April; occasionally as late as June or July.

Rhododendron canescens is similar morphologically toR.prinophyHum mAR.
periclymenoides, and these three variable species have been considered difficult to
identify by previous workers (Rehder, 1921; Skinner, 1955,1961; King, 1977a, b, 1980;
Galle, 1985). In addition, hybridization can occur where the habitats and geographic
ranges of these species overlap. All three species have pink-white corollas, and flower
before or with the leaves in the spring. In general, the corolla tube expands gradually
into the limb, but in R. canescens the limb is slightly more abruptly expanded than in
R. periclymenoides orR. prinophyllum. This character is difficult to measure on
herbarium material, and, in this group, is continuously variable. In the past, the
characters used to distinguishR. canescens fmmR. periclymenoides were primarily those of
the indumentum of the corolla tube (Rehder, 1921; Skinner, 1955,1961). Rhododendron
canescens has multicellular gland-tipped hairs on the outer surface of the corolla tube,
whereas most populations of R. periclymenoides have multicellular eglandular hairs.
However, there are glandular forms of R. periclymenoides. These were attributed to
hybridization by Skinner (1961). Other characters used to distinguish R. canescens from
R. periclymenoides include the following: dense unicellular pubescence of the abaxial
surface of the leaves (Porter, 1889a; Rehder, 1921; Skinner, 1961) and dense unicellular
pubescence of the abaxial surface of the bud scales (Rehder, 1921; Lawrence, 1954;
Skinner, 1961; Galle, 1968). Galle (1968) noted that R. periclymenoides is rarely white,
while R. canescens often has at least some white on the corolla limb, if not also on the
corolla tube. The gradually expanding corolla tube and the less dense unicellular
pubescent condition of the leaves of some individuals of R. prinophyllum have led to
some confusion in separating it from R. periclymenoides. These two species are more
northern in their distribution than R. canescens and are sympatric throughout much of
their range. Although Rehder (1921) recognized these as distinct species, Weigand (1924)
commented that one species graded into the other, and thus recognized R. prinophyllum as
a variety of R. periclymenoides [ R. nudiflorum (L.) Torrey var. roseum (Lois.)
Weigand]. Lawrence (1954) discussed the differences between the two species, and
distinguished R. prinophyllum from R. periclymenoides on the following characters:
unicellular pubescent bud scales vs. usually glabrous bud scales, blue-green adaxial
leaf surface vs. bright green surface, 'spicy9 fragrance vs. sweet fragrance, multicellular gland-tipped hairs on the surface of the corolla vs. multicellular eglandular hairs, shorter stamens and the fruit with multicellular glandular hairs vs. longer stamens and the fruit with multicellular eglandular hairs. Skinner (1961) also reported that plants of R. prinophyllum were generally non-stoloniferous, whereas those of R. periclymenoides were often stoloniferous. 306 EDINB. J. BOT. 50(3) Fig. 27. Distribution of Rhododendron canescens. The results of principal component analysis of 117 OTUs using 26 floral characters (see Table 5, Fig. 28) show that R. prinophyllum is morphologically the most distinctive of the three pink to white early flowering species. The characters which influenced the first principal component were primarily those of floral indumentum and size. Among the floral characters influencing the first component, sepal margin and pedicel pubescence were the most heavily factored. In R. canescens and R. periclymenoides the sepal margin is usually setose, whereas the sepals of R. prinophyllum usually have at least some multicellular gland-tipped hairs along the margin. In addition, the pedicels of R. prinophyllum are more often glandular than those of R. canescens or R. periclymenoides. It is interesting to note that when these indumentum characters are considered individually, R. prinophyllum is usually more distinct from R. periclymenoides, with which it is often sympatric, than it is from the allopatric R. canescens. Even though the range of morphological variation within each species overlaps to some extent, the overlap is consistently less between R. prinophyllum and R. periclymenoides than between R. prinophyllum and R. canescens. The delimitation of R. periclymenoides and R. canescens is less definite. These two species are generally allopatric but their geographic ranges overlap as R. canescens extends into the Piedmont and R. periclymenoides is found on the northern Atlantic Coastal Plain. The results of principal component analysis of 88 OTUs using 30 floral and bud-scale characters (see Table 5, Fig. 29) show that these two species are indeed very similar morphologically. The first component is most heavily influenced by corolla size, while the second is influenced most by the stamen length and sepal margin. Rhododendron periclymenoides has a greater percentage of individuals with pedicels lacking unicellular hairs than R. canescens, which always has pedicels with unicellular hairs. While the pedicels of R. canescens and R. periclymenoides usually have multicelluar eglandular hairs, R. canescens also often possesses at least some multicellular gland-tipped hairs on the pedicel. Since the indumentum of the corolla tube has been stressed in previous treatments this character was investigated with respect to its geographical distribution and its occurrence in the principal component analysis plot. The occasional glandular condition of the corolla tube of R. periclymenoides does not correlate with overlap of the geographic ranges of R. canescens and R. periclymenoides. Instead, it occurs sporadically in populations throughout the range of R. periclymenoides, often where R. canescens does not occur. Therefore the glandular condition of some individuals of R. periclymenoides reflects natural variation within the species, and usually does not indicate hybridization with R. canescens. However, the morphological similarity between these two species, whose ranges are primarily allopatric, raises the question of whether they should be considered to be geographical subspecies. This can best be answered by the results of the cladistic analysis (see Phylogenetic Analysis). Rhododendron periclymenoides and R. canescens form a paraphyletic group and therefore it would be phylogenetically misleading to lump both taxa into a single species. Therefore two partially sympatric species are recognized: Rhododendron periclymenoides and R. canescens. The most variable characters of R. canescens are the density of the pubescence of the leaves, flower colour, and, to a lesser extent, bud-scale margins. Plants in southern Georgia, Arkansas and Oklahoma tend to be very densely unicellular pubescent, whereas those individuals in Louisiana and Mississippi tend to be more sparsely unicellular pubescent. The flower colour varies from completely white to dark pink, but these variations do not show any geographical or ecological pattern. The margin of the bud scales is almost always ciliate, except for some populations in central Georgia and South Carolina. In these populations the bud-scale margins are hiixed unicellular-ciliate and glandular. Whereas R. canescens and R. prinophyllum are almost completely allopatric, the geographic range of R. canescens overlaps with that of R. periclymenoides. Rhododendron canescens is generally found in wetter habitats than R. periclymenoides, but this is not always the case, especially in the upper Piedmont. Rhododendron canescens hybridizes with several species that occur within its geographic range.

Notes

Named after the mountain on which it was found.

Transferred from Pseudovireya (sensu Sleumer 1966) as the bract margins are scaly, not hairy. At present known only from the type collection and not in cultivation. Said to be closely related to R. pulleanum (Kores 1978) but R. capellae has much less warty twigs, much longer, subulate outer bracts and an ovary which is both hairy and scaly. It would appear to be closer to R. womersleyi but differs in the more slender subulate bracts in addition to the characters used in the key.

Notes

Named after the mountain on which it was collected.

Not so far recollected and never cultivated. Very similar to R. syringoideum, differing chiefly in the much smaller flowers; it is the older name and would take precedence if the species were amalgamated.

Notes

Closely allied to R. haematodes but generally with larger leaves and calyces. One specimen, Forrest 20908, has the leaf shape and indumentum of R. catacosmum but the setulose young shoots and petioles of R. haematodes subsp. chaetomallum. This may be a hybrid. A specimen, Rock 17016, is intermediate between R. catacosmum and R. coelicum, with the sparsely stipitate-glandular petioles of the latter and the tomentose ovaries and the large calyx of the former. R. catacosmum apparently hybridises with R. citriniflorum (q.v.) and R. temenium.

Notes

A distinctive species though apparently hybridising with R. ponticum (q.v.) and R. smirnowii. The plate accompanying the type description gives a false impression of the species as described here and may be disregarded as there is no direct reference to any of the type specimens cited. Plate 3422 in Bot. Mag. 62 (1835) is a reliable representation of the species as treated here.

Notes

The inflorescences with several flowers and hairy pedicels recall R. henryi, but the hairs of the pedicels form a fine pubescence in contrast to the glandular patent hairs of R. henryi. Also the leaves are longer and narrower than those of R. henryi.

Notes

Subsp. platyphyllum is, essentially, a large-sized variant of subsp. cephalanthum, reasonably distinct both morphologically and geographically. Cytological observations on the two taxa would be interesting, but subsp. platyphyllum is not available in cultivation.

Distribution: Indonesia, S Sumatra, near Bengkulu (Benkulen): Mt Kaba (Mt Belirang). Mt Belirang does not appear on modern maps. Bele­rang is the Indonesian for sulphur, and the local people harvest sulphur on Mt Kaba and often call it Mt Belerang. It seems most likely that Belirang and Kaba are one and the same place.

Notes

The leaf margins of a number of species of section Choniastrum bear ciliate hairs in juvenile (or sucker) plants, but R. championae is the only species in which the adult leaf has marginal cilia. R. championae var. ovalifolium Tam (Survey Genus Rhododendron S. China 112, 1981) has bullate leaves, white flowers and some basal puberulence on the style.

Nomenclature

Rhododendron charitopes subsp. tsangpoense (Kingdon Ward) Cullen

Habitat: Slopes, rocks, open mountainsides

Distribution: China (S Xizang)

Altitude: 2450-4100m

Notes

Subsp. tsangpoense is a northern vicariad of subsp. charitopes; though they do not overlap geographically, they approach very closely, and there is no very clear morphological separation between them. The name curvistylum has been applied to a plant collected at the locus classicus of tsangpoense, which is in no way different from the type of the latter. However, material cultivated as R. tsangpoense var. curvistylum (often as Kingdon Ward 5843) is different—it is a plant with very small, narrowly elliptic, acute leaves, and is probably a hybrid between subsp. tsangpoense and R. campylogynum.

Notes

Named after Konrad H. Christ, Swiss fern specialist who was professor of botany at Basel.

The records from near Wamena are a surprising extension to the range of this species which had previously been known only from Papua New Guinea; some of these plants differ in having broadly tapering leaf bases but others are quite typical with cordate bases. Those with tapering leaf bases could be hybrids with R. curviflorum. It is reported hybridising with R. beyerinckianum (van Royen & Kores 1982), these hybrids having uniformly pink flowers (see R. x schoddei).

Notes

This species, which is known from only two wild-collected specimens and material in cultivation, is peculiar in several respects. It was described from cultivation and said to be raised from seed of Forrest 25446—a flowering specimen from Yungchang in Yunnan belonging to subsection Maddenia, and here identified as R. yungchangense (p. 53). The cultivated material is certainly not yungchangense, but appears to combine most of the characteristics of subsection Boothia with a few of subsection Maddenia, particularly scale type, calyx form, the large size of the flower and the presence of indumentum at the base of the corolla tube outside. On the basis of this evidence the plant might well have been regarded as a natural hybrid between yungchangense and sulfureum. However, in the same year that the plant first flowered in cultivation (1931), Kingdon Ward collected a specimen in the Adung valley on the Burmese/Chinese frontier, which matches it in every respect. The Adung valley is about 240 km north of Yungchang and was not visited by Forrest, so this does not explain the origin of the material in cultivation. It is possible that chrysodoron is distributed between the Adung valley and Yungchang, or that it is the result of occasional hybridisation between members of subsections Maddenia and Boothia, thus explaining the scattered distribution as we know it today. The description above has been drawn up from wild material; in cultivation the flowers may be larger (up to 40 mm) and, apparently, of a deeper yellow.

Notes

R. ciliicalyx is a reasonably uniform species. R. missionarum is in no way different and probably comes from the same general area (the localities given by Maire have not been precisely identified). R. pseudociliicalyx was described from a cultivated specimen; it is also identical to R. ciliicalyx and is likely to have originated in Yunnan rather than Sichuan as surmised by Hutchinson (loc. cit.)

Notes

Another obscure species. The paratype cited by Hutchinson with the original description [Forrest 25484) is very different from the type, and is here placed in R. pseudociliipes (p. 50). R. ciliipes is very similar in foliage to R. roseatum, also from the Shweli/Salween Divide, but it has an impressed style.

Habitat: In open montane shrub­beries especially in disturbed areas at roadsides.

Distribution: Indonesia, New Guinea (W), Wissel Lakes, 2400m, and on the southern side of Mt Jaya (Carstensz).

Notes

Latin – Cinchona – a South American plant in the Rubiaceae from which was derived the antimalarial ‘quinine’; florum – pertaining to the flower. The flowers are reminiscent of those of the quinine plant.

Notes

The corollas of subsp. xanthocodon are campanulate and vary in colour from clear yellow to apricot, yellow flushed with purple (either when young, when old, or permanently), or purple. The subspecies intergrades with subsp. cinnabarinum in Bhutan, where many intermediates occur.

Notes

The two extremes, var. citriniflorum with yellow flowers, a short calyx and glandular ovary, and var. horaeum with red flowers, a well-developed calyx and a tomentose, eglandular ovary, are distinct. There is however a range of intermediates (var. horaeum as recognized here includes plants with flowers that are orange or tinged with red). The intermediates fall into two groups. The first, with yellowish-red flowers and glandular ovary, includes plants referred to R. citriniflorum subsp. rubens Cowan (Notes R.B.G. Edinb. 20: 14, 1940, type: Rock 23245, E) and the following: Forrest 21859; Rock 10109, 10111, 23669. The second group, with yellow flowers and an eglandular ovary, include: Forrest 25595; Rock 10106, 22189, 22277.

Notes

A distinctive species, the only one in subsection Taliensia with a consistently 7-lobed corolla. A specimen from S Xizang, Ludlow, Sherriff & Taylor 3868, is technically referable to R. clementinae on account of its 7-lobed corolla but it has an apiculate leaf with a thin white indumentum beneath and white-tomentose petioles. Without further material, the taxonomic significance of these differences remains uncertain but the locality is considerably further west of the present known range of the species.

Notes

Closely allied to R. pocophorum but differing in its broader leaves and non-tomentose petioles. One plant, Kingdon-Ward 13150, is intermediate between and may be a hybrid of R. coelicum and R. haematodes subsp. chaetomallum. It not only has the stipitate glands of the former but also the setae on the young shoots and petioles of the latter.

Notes

Latin – caelestis – heavenly; no doubt an impressive plant.

Still a poorly known species but distinctive in its prostrate habit and spirally arranged leaves. Sleumer (1973) commented that it might have to be united with R. schizostigma and R. disterigmoides but both of these species have a much more vigorous erect habit.

Notes

Said to be named after the author’s wife!

Van Royen & Kores (1982) reduced R. pseudonitens to this species on the basis of field work which showed the size difference between them was untenable. They also recorded wild hybrids with R. culminicola and R. womersleyi in the Finisterre Mts and with R. macgregoriae in the Tari Gap.

Notes

Sleumer (1966) noted: ‘Much related to R. lochae F. v. M. from NE Queensland (the only Rhododendron in Australia [at that time]), which, however, has red corollas, laxly hairy ovary (the scales thus clearly visible) and 2–5 (rarely up to 7) flowers per umbel’. It would be interesting to know if DNA analysis supported this view.

Notes

The species is fairly distinctive, with its scattered elliptic leaves with no obvious lateral veins but often drying with oblique lateral folds on the undersides of the blades. This has been confused with R. giulianettii but that species has much broader leaves in relation to length, with rounded rather than tapering bases. Rhododendron giulianettii also commonly (but not always) has leaves with 1–2 lateral veins per side, visible.

Rhododendron comptum var. trichodes Sleumer

Differing only in that the ovary is hairy, as well as densely scaly. Described with bright red flowers. Fruit 10–12 x 6–7mm, becoming erect with persistent styles. Seeds 20–25mm, without tails 0.9mm, the longest tail 0.9mm.

Distribution: Papua New Guinea, Mt Albert Edward, cliffs in open grassland and terrestrial on a steep, boggy slope

Altitude: 3600-3800m

Notes

Greek – tricho – hairy, alluding to the hairy ovary which distinguishes this from the type variety.

Nomenclature

Rhododendron concinnoides Hutchinson & Kingdon Ward

Very similar to R. monanthum, differing essentially only in its purple corolla. INDIA (Arunachal Pradesh)

Notes

Known only from the type collection, this species is a purple-flowered equivalent of R. monanthum. Its distinctness is dubious (purple/yellow corolla colour variation is known in other species, e.g. R. lepidotum, see p. 149) and further material is necessary before its status can be settled.

Notes

A rather variable species known from material that is, for the most part, poor. Leaf shape and size vary, as does the colour of the leaf undersurface. It is, however, reasonably distinct on the basis of its broad leaves and lepidote, purple corolla. R. apiculatum was based on a poor specimen collected by Wilson, and is identical with R. concinnum except that the extant fragment of the corolla is not lepidote. The varieties recognised by Davidian have no significance other than in horticulture. I have seen no material of R. hutchinsonianum Fang, Acta Phytotax. Sinica 2:83, 1953 (type: Szechuan, Erh-lang-shan, Tien chuan hsien, Hu & Ho 10148, holo. CHENGDU). From the description, it is merely a variant of R. concinnum.

Notes

R. coriaceum is allied to R. rex but may be distinguished from subsp. rex, which also has a pale leaf indumentum, by its more slender leaves and its more westerly distribution. Some forms of subsp. fictolacteum approach R. coriaceum in the size of their leaves but have a consistently darker indumentum.

Habitat: Sub-alpine forest, marginal forest shrubberies and in open vege­tation, also on ridge crests, commonly on mossy or peaty soil, locally abundant

Distribution: Indonesia, New Guinea (W), the Main Range from Mt Jaya (Carstensz), Hubrecht and Orange Mts to Mt Trichora (Wilhelmina).

Altitude: 3100-4300m

Notes

Resembling Correa, Australian trees in the Rutaceae.

Introduced into cultivation in 1993 by Paul Smith, it grows weakly as a leggy shrub in Edinburgh although flowering regularly. It is one of the species used in the Mt Jaya mine to recolonise disturbed ground and spoil heaps as it grows well at high altitude. It is not a spectacular plant, the flowers being rather small. It comes in two colour forms, yellow and orange, although intermediates may occur.

Notes

A distinct species of rather uncertain affinities. It was originally placed in subsection Trichoclada (Trichocladum series) because of its deciduous leaves, but it differs from that group in scale type and inflorescence, and is more closely allied to R, lepidotum.

Notes

Rhododendron crassifolium is a variable but nevertheless very distinct species. Hybrids with R. stenophyllum have been recorded and are very similar to R. nervulosum. Rhododendron x planecostatum is the hybrid with R. bagobonum. Rhododendron brevitubum was reduced to synonymy by Argent et al. (1988). It differed by the hairs inside the corolla tube being in 5 distinct vertical stripes. The hairs inside the corolla of R. crassifolium are commonly in 5 indistinct stripes and in other ways the plants are very similar: at best R. brevitubum could be considered as a local variant.

Notes

R. crinigerum is less setose that the remaining species of this subsection and in this respect approaches some members of subsection Taliensia. However, in leaf shape and in leaf characters, it is closer to the remaining members of subsection Glischra.

Rhododendron crinigerum var. euadenium Tagg & Forrest

Notes

The leaves of all the specimens of var. euadenium are more glandular than those of var. crinigerum and most are less densely hairy. The type, however, is more densely tomentose. The following specimens are intermediate between the two varieties in that the lower surface of the leaves is densely tomentose but also with many stipitate glands: Rock 10967, 22504.

Notes

This is an obscure species in many ways. There is no herbarium material from the wild and it
is known only from cultivated material. Young plants were reputedly collected by Lady Cuffe on Mt
Victoria in Burma and grown on at Glasnevin, Dublin. The notes with the type description in the
Botanical Magazine suggest that the place of origin was Sindaung on the edge of the Shan plateau,
but this was later altered to Mt Victoria by Hutchinson. The swollen stem base, which is
illustrated in the Botanical Magazine plate appears to be unique in this group of rhododendrons.
Hutchinson's two descriptions (Bot. Mag.y cited above, and Notes R.B.G. Edinb. 12:52, 1919) do
not agree entirely with material at Edinburgh said to come from the type plant and determined by
him: for instance, in this material the corolla is sparsely lepidote all over, not 'not lepidote
except towards the 5 lobes which are sparingly so towards the middle'; and thestyle is pubescent and lepidote at the base, not just lepidote. I have not been able to trace a type specimen, so this matter cannot be resolved.

Habitat: Low mossy forest or the margins of sub-alpine shrubberies, open slopes or summit vegetation, also found in alpine pasture, in both primary and secondary communities, often as part of the forest undergrowth, locally plentiful.

Distribution: Indonesia and Papua New Guinea. Widespread on the island of New Guinea on the Main Range, from Mt Jaya (Carstensz) to the Southern and Western Highlands and in the Owen Stanley Range, also in the Mt Saruwaged–Rawlinson Range area.

Altitude: 2400-4000m

Notes

Rhododendron culminicola is conceived here in the broad sense of Sleumer (1966) with the exception that the variety nubicola has been reinstated as a good species. Specimens from the upper montane forest (at the lower elevations from c.2400m) tend to have larger flowers and tapering leaf bases. Forms at higher elevations (3200–4000m) have smaller flowers and smaller, stiffer, short-petioled or sub-sessile leaves with rounded or sub-cordate bases. It is one of the small number of variable species which are distributed all over the mountainous part of New Guinea.

Distribution: Western most Virginia and eastern Kentucky in the Cumberland Mountains and Plateau, south through Tennessee to northern Alabama, and east of the Tennessee River Valley in the southern Blue Ridge, along the border of Tennessee and North Carolina, south to northern Georgia. Isolated populations occur in Talladega, Cleburne and Randolph counties in Alabama

Altitude: Around 900m

Illustrations:

Galle, 1985 (photo)

Notes

The name R. bakeri (Lemmon, 1938) has been used for this diploid flame azalea since
Skinner (1955) considered R. bakeri to be the same taxon as R. cumberiandense. Since R.
bakeri, was an earlier name, it was properly used over R. cumberiandense. However, the
type specimen of Azalea bakeri (= R. bakeri) is not at all similar to the type of R.
cumberiandense. The specimen, which is labelled Azalea bakeri by Lemmon, has young
expanding leaves, which are densely pubescent on the abaxial surface. In addition, the
margins of the floral bud scales are all unicellular-ciliate, and the corolla possesses
both glandular and eglandular multicellular hairs. None of the above characters is found
in R. cumberiandense, which flowers well after the leaves have expanded and usually has
glabrous leaves (never densely pubescent). In addition, the floral bud-scale margins and
the outer surface of the corolla are consistently glandular in R. cumberiandense.
Therefore Lemmon's specimen is probably a hybrid between R.flammeum and R. canescens (see hybrid names, p. 362). Thus, the correct name for the diploid flame azalea is Rhododendron cumberiandense.

Chromosome number: 2n = 26 (Li, 1957; WEEngham, 1973).

Rhododendron cumberiandense is most closely related to R. calendulaceum (see Phylogenetic Analysis) and can be distinguished from the latter by its flowering well after the leaves have expanded, and by the eglandular condition of the pedicel and sepal margins. In addition, the leaves are very glaucous abaxially, and often are bluish green to dark olive-green in colour, especiaMy upon drying. This species is primarily restricted to the Cumberland Mountains and Plateau, where it is morphologically and phenologically distinct from R. calendulaceum. In the southern Blue Ridge, however, R. cumberiandense can hybridize with R. arborescens or R. viscosum. It can also occupy the same kinds of habitats as high-altitude late-flowering individuals of R. calendulaceum. In these areas it is more difficult to distinguish R. cumberiandense from R. calendulaceum (see discussion under R. calendulaceum). See Appendix for citation of representative hybrid specimens.

Notes

A distinctive species, in many ways similar to the species of subsection Heliolepida (p. 87), from which it differs mainly in the possession of a large, deeply Iobed calyx. It is in many ways (large, zygomorphic flower, type of scaling, etc.) aberrant in subsection Lapponica, and stands in an intermediate position between Lapponica and Heliolepida. The Philipsons (1975, p. 16) note the occurrence of natural hybrids with R. hippophaeoides and other, undetermined, species.

Notes

Sleumer (1966) notes: ‘The size of the corolla in Smith’s description of 1914 differs from that in t.36 B; unfortunately, the type material, conserved in formaline at Bogor, is practically useless. I have drawn a new description of it based on good and apparently conspecific specimens (BRASS 11215 AND 11536) from the Bele R., which have yellow flowers instead of “lilac” as said of the type mater­ial, which came from the Keyts Mts. Also the description of the perulae [bracts], not given in the original diagnosis, is made after the BRASS collections’. I have followed Sleumer’s interpretation of this species; the anatomical characters certainly agree closely with Smith’s descriptions but I cannot find the discrepancy in measurements that he mentions. Rhododendron curviflorum was common around the village of Pabilio above Wamena and was all very uniform yellow in colour. It would be odd for this species to occur in the lilac mentioned in the original type description. This may have been an error in the field descriptions or we may still be dealing with two different species. Further collecting in the Keyts Mts will need to be done to resolve this.

Notes

Superficially close to R. thomsonii but differing in the paler flowers and the mammillate leaf epidermis. Var. eriphyllum, which is only known from the type and differs only it its sparsely glandular ovary, is not worthy of formal recognition.

Rhododendron dalhousiae Hooker

Epiphytic or more rarely free-growing shrub. Young shoots loriform-setose. Leaves mostly narrowly elliptic, more rarely tending to obovate, (75-)100-170 x 35-70 mm, tapered to the base and to the ± rounded apex, petioles variably loriform-ciliate, lower surface greyish or brownish green with small, slightly unequal, reddish scales more than their own diameter apart; margins often crenulate. Inflorescence 2-3-flowered, pedicels 15-20 mm, lepidote and pubescent, accrescent in fruit. Calyx conspicuous, deeply 5-lobed, the lobes oblong or oblong-triangular, rounded at the apex, 10-15 x 5-10 mm, lepidote at the base, the middles of the lobes with few to many filiform-acicular hairs. Corolla narrowly funnel-campanulate to funnel-campanulate, white or cream, often yellowish inside, sometimes with 5 red lines running from the base of the tube to the apices of the lobes, 85-105 mm, tube 60-75 mm, very sparsely lepidote to elepidote outside. Stamens 10, filaments pubescent in the lower part. Ovary lepidote, tapered into the style which is lepidote in the lower part. Capsule cylindric-fusiform, 40-50 x 15-20 mm, lepidote, rather strongly 5-ridged.

Notes

Named after Datianding, the place of the original collection.

Flowers June, Fruit Oct.

Said to be similar to R. rupivalleculatum but differing in the oblong-elliptic leaves, 2–4 x 1–2cm; the leaf apex obtuse, not recurved; the inflorescence of a 4–7- flowered umbel; the stamens and pistil much shorter, and the ellipsoidal capsule. Very reminiscent of R. rushforthii in the umbellate inflorescence. The much smaller vegetative measurements may be accounted for by differences between growing in cultivation and in a harsh wild environment but the lack of description of the indumentum on the ovary and style leaves doubt about the identity of this species. Only an examination of the type specimen will settle the matter of whether these two species are truly different. Rhododendron datiandingense is the older name by a few months and would take precedence if they are found to be conspecific.

Notes

R. dilatatum var. satsumense is described as differing from R. decandrum in its dilatate-ovate leaves, shining above, in the involucre being lightly reflexed before anthesis, in the glabrescent floral buds and in the glandular-punctate, usually not ciliate, capsules. We assume that this taxon has ten stamens since it has been allied by the original author to R. decandrum; we have not however seen any material of it.

Notes

The colour of the stylar glands is not clear in all herbarium specimens. The pubescent stamens have therefore been used for differentiating R. decorum from the closely related R. vernicosum. Some ± intermediate plants occur in one or two localities, suggesting local hybridisation (Rock 24619, 25172, etc.). Some specimens (e.g. Forrest 11916ScFarrer979) approachR. diaprepesm the size of their corollas or leaves; these apparently occur at lower altitudes than is usual for R. decorum. One specimen (Rock 16474), assumed to be a hybrid of R. decorum, differs in its sparsely dendroid-tomentose ovary and style base with glands extending only half way up the style.

Notes

Known only from the type collection. A specimen hitherto identified as R. sulfureum (Burma, Kaw-ji pass, 10500 ft, Farrer 1550) has scales which match those of dekatanum; in other respects it is typical of sulfureum, and its status is uncertain.

Notes

Nomenclature

Rhododendron dendricola Hutchinson

Epiphytic or free-growing shrub. Young growth rarely loriform-setose. Leaves narrowly elliptic to narrowly obovate, tapered to the base, rather abruptly acute or with a short drip-tip, 70-120 x 30-48 mm, undersurface with a covering of scales of variable density. Calyx disc-like or very obscurely lobed, not loriform-ciliate. Corolla white, often with a yellow, orange or greenish blotch and/or flushed pink, lepidote outside, pilose at the base of the tube. Ovary lepidote, usually waisted towards the apex. Capsule up to 20 mm.

Notes

A very variable species in terms of indumentum, density of scales and corolla colour; all this variation is, however, continuous. Its distribution is rather disjunct, with one main mass of records in the Taron valley (c. 28° N), the other further south in the Salween valley (c. 25-26° N). In spite of this, no clear distinction into two units can be made.

Notes

Flowers Sept.–Oct., although one plant was flowering in June. The fruit said to be ripe Sept.–Oct. of the following year.

Very similar to R. emarginatum but with consistently smaller, narrower leaves which gradually broaden upwards to near the apex. It also has hairs on the ovary as well as scales. It might be thought to be a high altitude form of R. emarginatum except that this species is reported at even higher altitudes than R. densifolium. These two species do grow together in the wild and are clearly distinct on leaf size. The marginal hairs on the bracts are exceptionally short, barely reaching 0.1mm. Recently introduced into cultivation but not yet known to have flowered.

Notes

Only known from material collected by Farges near the type locality. The bullate leaves and leaf indumentum suggest a distant affinity with R. mltonii but the glandular ovary and well-developed calyx suggest that it is closer to R. adenogynum and its immediate allies.

Distribution: Indonesia, New Guinea (W), above Jayapura on the W slope of Mt Dafonsero; Cycloop Mts, Faita R. camp and along path from Ifar to Ormu.

Altitude: 500-1400m

Notes

Named after the genus Dianthus because the flowers have a similar perfume.

In cultivation since 1961 when Professor Sleumer sent seed from New Guinea to the USA from where it has been distributed. Probably all genuine materials of this species are from this introduction. Slow growing and fairly compact.

Notes

Closely allied to R. decorum but with larger leaves and corollas, also close to R.faithae(q.v.)

Further material seen since the completion of the manuscript suggests that R. diaprepes is best treated as a subspecies of R. decorum as several intermediate specimens are now known from the extreme western part of Yunnan, within the range of R. diaprepes. The necessary combination is R. decorum Franchet subsp. diaprepes (Balfour f. & W. W. Smith) T. L. Ming, based on R. diaprepes as cited above.

Habitat: Epiphytic on tall trees in ravines and wooded slopes, in dense shade, terrestrial in secondary grassland and along roadsides

Distribution: Papua New Guinea, Upper Sepik R. region; Kani, Finisterre and Saruwaged Mts. Common in the Eastern Highlands, also in the Simbu and Western Highlands. Possibly in W New Guinea; see notes under R. bryophilum.

Altitude: 1200-1940m

Rhododendron dielsianum var. stylotrichum Sleumer

Slender erect shrub to 3m. Corolla pink. Differs from var. dielsianum by the style which is laxly shortly hairy with spreading hairs in its lower ½.

Notes

A variable species. Specimens from open habitats are significantly smaller, with shorter corollas and leaves. There also appears to be considerable variation in the amount of indumentum on the ovaries.

Notes

This species is apparently intermediate between subsections Irrorata and Neriiflora; the corolla suggests an alliance with the former and the well-developed calyx with the latter. R. dimitrium might be a hybrid between R. irroratum and R. neriiflorum, both of which occur in the vicinity of Dali. However, the five specimens seen suggest that a stabilised population has developed thus meriting formal taxonomic treatment.

Notes

Latin – aster – a star; montes – mountains. Alluding to the Star Mountains where it has been collected.

Differing from the type subspecies chiefly in the distinctly pseudowhorled leaf arrangement.

Rhododendron disterigmoides was described from the Lake Habbema area in West New Guinea, not a great distance from the locality of this subspecies. The type of ssp. disterigmoides was described incompletely in that the flower buds were not collected. It is possible that flower bud characters from the type area will show sufficient difference from those of this new subspecies to warrant that this taxon be raised to specific level. Apart from the difference in leaf arrangement there are some other minor differences: the leaves of this subspecies are less revolute, the margins being so only in the proximal 1⁄3, the apices are often obtuse rather than acute to acuminate, and the leaf bases are often broadly tapering rather than rounded or sub-truncate. This subspecies has been confused in the past with R. pulleanum. It is easily distinguished on the marginal bud scale indumentum which is of simple hairs in R. pulleanum, not scales.

Notes

A distinctive species on account of its often acuminate leaves and well-developed calyces. The calyx is reminiscent of that found in subsection Thomsonia and it is possible that this taxon is a hybrid.

Notes

This species is extremely variable throughout its entire range but may be known amongst the section Malayovireya by its short petioles and the relatively long, tubular, mostly orange-red flowers which are without scales or only slightly scaly at the base and aggregated together into umbels of 10 or more. I have never seen yellow-flowered specimens and this report may be an error although there are occasional purplish-pink-flowered populations which are similar in colour to many of the forms of R. malayanum. A puzzling aspect of this species is the variable shape and size of the flowers. A population in a peat swamp area in southern Sabah had three distinct size classes of flower – large, intermediate and small – which did not appear to intergrade and were all growing together. It is closely related to R. fallacinum, which is maintained in this account although distinguished with difficulty from the complex variation that occurs in R. durionifolium. Rhododendron fallacinum usually has a shorter corolla tube and the flowers are densely scaly outside, with scales occurring right up onto the backs of the corolla lobes. Slender forms of ssp. sabahense approach R. malayanum in form but the petioles do not get quite as long as in that species, the flowers are more numerous from a single flower bud and R. durionifolium never normally produces lateral inflorescences. Rhododendron acuminatum could also be confused but apart from occurring at higher altitude, this species has more strongly puckered leaves with the lateral veins deeply impressed on the upper side and like R. malayanum it has much longer petioles than R. durionifolium.

Differing from the type subspecies in the more slender, narrowly elliptic to elliptic leaves, 90–160 x 20–50mm, with a tapering base; longer petioles: 4–7mm; leaves which are greener and more quickly glabrescent above and flowers predominantly pink or red rather than orange in colour.

Altitude: 900-2400m

Notes

Latin – Sabah – the country; ensis – place or origin. Coming or originating from Sabah.

This subspecies occurs above 900m in fairly uniform populations on Mt Lumarku, Mt Lotung and near Long Pasia, in the Sipitang District. With its red or pink flowers and long corolla tubes it would be suitable for bird pollin­ation but this has not been observed. The only hybrid seen is with R. micromalayanum on Mt Lumarku and in the Long Pasia region. This subspecies has been cultivated since 1980. It grows slowly but has most attractive flowers.

Notes

R. eclecteum hybridises with R. pocophorum (see under R. x hemigynum). Kingdon-Ward 6900, with leaves typical of R. eclecteum except that they have a floccose but persistent indumentum, may also be of hybrid origin.

Rhododendron eclecteum var. bellatulum [Balfour f. ex] Tagg

Petioles 8-30mm; leaf lamina 6-12.5 x as long as petioles, usually lacking simple hairs; corolla usually white to yellow, sometimes flushed with rose

Notes

Flowering specimens with relatively long petioles and elliptic leaves almost always have pale flowers but well over half the specimens seen lack flowers or flower colour notes. Therefore, the status of var. bellatulum, which apparently intergrades with var. eclecteum, will remain uncertain until field studies are carried out.

Nomenclature

Rhododendron eclecteum var. eclecteum

Petioles 4-10mm; leaf lamina 11-18 x as long as petioles, at least some simple straight hairs usually present near the midrib; corolla usually deep magenta-rose to crimson

Notes

Cowan & Davidian (loc. cit.) state that var. brachyandrum differs from var. eclecteum in its darker flowers. However, there is no indication of the flower colour of the type of var. eclecteum, or indeed of the majority of the herbarium specimens seen. The type of var. brachyandrum has small flowers, the diagnostic character used by the original authors, although, like Cowan & Davidian, 1 consider that to be of little taxonomic significance. If var. eclecteum is restricted to plants with relatively short petioles and deeply coloured flowers then the following specimens are intermediate between vars. eclecteum and bellatulum: Forrest 18023, 25603; Rock 8748, 8750, 9205, 22222, 22224, 22230, 22661, 22664, 22665.

Rhododendron edanoi subsp. pneumonanthum (Sleumer) Argent

Shrub or small tree to 3m. Scales blackish-brown. Lateral veins 5–9 per side, straight or curving away from the mid-vein and disappearing before the edge of the leaf, hardly raised but usually distinct both above and below and without visible reticulation. Petiole 1–3 x 3–4mm, dark red, often broader than long and with dark-brown scales, weakly grooved above.

Notes

Rhododendron pneumonanthum has been reduced to a subspecies of R. edanoi (Argent 2004). Sleumer (1966) distinguished these two species: ‘Corolla tube more or less manifestly and gradually narrowed from the base upwards. Leaves sub-sessile [R. pneumonanthum] vs. Corolla tube equally wide all over or slightly and gradually widened from the base upwards. Leaves distinctly petioled. [R. edanoi]’. An examination of isotypes of the original collection of R. edanoi showed that the first character is not a valid difference. Several corolla tubes exhibit quite definite narrowing from the proximal to the distal ends. The corollas from cultivated plants from both Palawan and Borneo in the fresh state all quite clearly taper from base to mouth. After pressing, the tube can appear to at least look parallel sided. There is a difference in petiole length between Bornean and Philippine materials but again there is a good deal of variation even on one plant and this alone would not support maintaining these plants as different species. There is also a very small difference in the scales on the leaves from the two islands – those from Bornean materials are darker and more variable in size – but both have essentially the same sub-stellate shape, are tall and are set on pronounced epidermal tubercles. The vegetative habit of the plants in cultivation from the different islands is certainly very different. Both Philippine collections are slow and low growing compared with the tall, ‘leggy’ and much more vigorous Bornean plants. Differences in habit between different populations of the same species are known elsewhere (R. burttii and R. leptanthum). The clinching factor in regarding the Bornean R. pneumonanthum to be, at best, a subspecies and not specifically distinct from R. edanoi is the fact that the distinctive flower bud morphology is identical in plants from both Borneo and Palawan.

Notes

Latin – emarginatus – shallowly notched, alluding to the often emarginate tips to the leaves.

Professor Sleumer compared the types of R. euonymifolium and R. poilanei (Sleumer 1958) and reduced these species to synonymy. These types have also been examined for the present study and their reduction appears logical. Rhododendron leiboense was differentiated in having more slender branches, triangular calyx lobes and flowers in twos. It does not appear to warrant even varietal recognition on these characters. I have reduced R. maguanense after examining the type material. Feng (1983) said this species was close to R. emarginatum but differentiated it on its smaller leaves and longer calyx lobes. Neither of these characters are sufficiently significant. The calyx lobe development is considered variable in R. emarginatum and the smaller leaves with less conspicuous venation appear to be reduction due to exposure.

Rhododendron emarginatum var. eriocarpum K.M.Feng

Differing chiefly in that the ovary is both hairy and scaly. The calyx lobes are also well developed, 1.8 x 2mm, with scales along the margins of the lobes. Seeds 2.5–3mm, without tails c.1mm, the longest tail 1.2mm.

Distribution: Known from the type locality in China and Guangxi Province, Daimiaoshan Xian, Pingshixiang, Jiuwandai shan

Altitude: 1200-2180m

Notes

Greek – erio – woolly; carpon – fruit. Alluding to the hairy ovary.

Recorded flowering in Aug. and Oct. The hairy ovary is one of the significant characters separating R. emarginatum from R. insculptum. This variety confuses this distinction.

The leaves of var. eriocarpum are quite distinct in being less revolute and more distinctly tapering towards the base than those of R. emarginatum. It might yet warrant specific status.

Notes

Named after Victor G.A. Engler (1885–1917).

Very similar to R. baenitzianum but apparently distinct in the clearly revolute margin to the leaf and longer petioles. Baron von Mueller used the invalid name ‘megalo­stigma’ for this species which has extremely divided stigmatic lobes.

Notes

Greek – Erica – a genus of mainly South African shrubs; oides – indicating resemblance, the small leaves of this species being very like those of an Erica.

Flower and fruit Jan.–Dec.

Rhododendron x silvicola Sleumer (R. cuneifolium x R. ericoides) Rhododendrons of Sabah, Sabah Parks Publ. 1988. 8: 102. Type: J. & M.S. Clemens 30081, April–June 1932. Borneo, North Borneo, Mt Kinabalu, Tenompok, 5000ft (E, K). Derivation: Latin – silva – wood or forest; cola – inhabitant. An inhabitant of the forest since it was first thought to be a shade form of R. ericoides. Synonyms: R. ericoides var. silvicolum Sleumer, Reinwardtia 1960. 5: 62 (orthographic variant). R. x silvicolum Sleumer, Rhododendrons of Sabah 1988: 102 (orthographic variant). Shrub to 3m. Similar to R. ericoides but with larger leaves, 9–11 x 1.8–2mm, flowers red, usually with elong­ate calyx lobes. Malaysia (Borneo), Sabah. Fairly common on Mt Kinabalu around the zone of overlap between the two parent species. Recent records are all between 2800 and 3200m although the type collection was recorded at 1525m – this is possibly an error. A large shrub of this hybrid has persisted over more than 20 years beside the main trail up Kinabalu where it is very conspicuous.

Notes

Contrary to Ohwi's most recent statement in the new edition of his Flora of Japan, we are convinced that R. tamurae is a synonym of R. eriocarpum. R. tawadae is described as having small reddish-purple flowers; this agrees better with R. eriocarpum than it does with R. simsii, with which it has been synonymized in the past.

Notes

A rare species, the only specimens seen being those collected by Esquirol and Cavalerie. It has the smallest flowers and the smallest average leaf size of any species of the section. It falls within the group combining glabrous pedicels with (mainly) 1-flowered inflorescences.

Notes

The distinction between var. brunneifolium and var. mesopolium, as implied by the key, is of a fairly trivial nature but, despite this, var. mesopolium may be more distantly allied to var. brunneifolium and var. eudoxum than these two are to one another. Although it cannot be confirmed for certain from herbarium material, the corollas of var. mesopolium do appear to have been more fleshy and more obviously tubular-campanulate than those of the other two varieties. In these respects var. mesopolium is apparently closer to R. sanguineum and its allies.

Notes

R. fulvastrum var. albipetalum is apparently no more than an albino form of var. eudoxum. The young shoots of the types of both R. trichomiscum and R. trichophlebium are ± densely covered with stout setae as in R. temenium but otherwise are closer to R. eudoxum.

Young shoots and pedicels usually floccose-tomentose, eglandular, not strongly setose; leaves 3.5-7cm, with ± prominent veins and a thin whitish discontinuous indumentum beneath; corolla 30-35mm, rose-pink; ovary predominantly tomentose though sometimes also with a few glands.

Notes

This species has been traditionally allied to R. martinianum (subsection Selensia) but it differs in its campanulate corolla with nectar pouches, a character that excludes it from subsection Selensia. Several sheets cited in the type description are said to be referable to R. stewartianum (Cowan & Davidian, Rhododendron Yearbook 6: 177, 1952), which in some respects it resembles and of which it may be a hybrid.

Rhododendron evelyneae Danet

Erect shrub to 2m. Twigs cylindrical, 2–4mm in diameter, densely scaly and warty after the scales have fallen. Leaves erect, in pseudowhorls of 4–6 together, with some cataphylls along the internodes. Blade 20–60 x 10–30mm; apex acute to obtuse, with a hooked point that often falls early to leave a small callosity; margin entire, strongly revolute, the sides often being bent into a tube; base rounded to cordate; upper side at first densely scaly and rough, the scales quickly falling then remaining rough from the scale bases, green; lower side densely and more persistently scaly and warty. Scales orange-brown, irregularly stellate, the centres small from a stalk mounted on an acute persistent protuberance. Mid-vein slightly impressed above and prominent below. Petiole 1–3mm, grooved above, rigid and rugose. External bracts triangular to ovate, caudate to cuspidate at the apex, scaly and rough and shortly hairy outside, scaly on the margin, glabrous inside; internal bracts to 25 x 20mm, obovate-obcordate to broadly spathulate-obcordate, apiculate or mucronate at the apex, glabrous or with a few hairs outside. Bracteoles 15mm, linear, broadened to spathulate distally, sub-glabrous. Inflorescence of 3–7 hanging flowers, without scent. Pedicels 20–30 x c.1.5mm, shortly hairy and densely scaly, rough with papillae. Calyx obliquely discoid, c.4mm in diameter, sub-entire, shortly hairy and densely scaly. Corolla 30–40 x c.25mm, pink, tubular; tube 23–31 x 7 x 12mm, straight or a little curved, sometimes slightly laterally compressed, hairy and scaly outside, distinctly hairy inside; lobes 7–12mm in diameter, half-spreading to spreading, overlapping to c.½, broadly elliptic to sub-circular, rounded or a little retuse at the apex, scaly outside except near the margins. Stamens irregular, exserted to c.5mm; filaments pink, shortly hairy at the base; anthers c.3 x 1.5mm, deep purple, oblong, with rounded bases to the cells. Disc 10-lobed, glabrous except at the top where it is densely short-hairy. Ovary c.5 x 3mm, ovoid, tapering to the style, densely short-hairy and scaly, the white hairs covering the reddish-brown scales; style red or pink, slightly exserted from the mouth of the flower, shortly hairy up to halfway; stigma 5-lobed. Fruit 20 x 8mm, ellipsoid-oblong, grooved, hairy and scaly, the valves a little or not curving on dehiscence. Seeds 4–5mm including the tails.

Distribution: Indonesia, New Guinea (W), at the watershed between Mt Yonowe and Mt Jayawijaya, on the Longimik lateral moraine

Altitude: 3140-3190m

Notes

Named after the author’s mother, Evelyne Danet.

Known at present only from the type collection.

Close to R. spondylophyllum but differing chiefly in: the longer petiole, 1–3mm (1mm); the pedicels scaly and hairy (scaly only) and the style shortly hairy in the basal 1⁄3 (hairy and scaly for c.2⁄3).

Notes

I have not seen the single reported flowering specimen and therfore hesitate to suggest an affinity for this species. If differs from R. irroratum subsp. kontumense (also from Vietnam), however, in its white flowers and styles glandular only at base.

Notes

Latin – exubero – to grow luxuriantly, referring to the wider leaves than those of the related R. nervulosum.

An unusual species confined to very wet mossy forest in the wild. It was introduced into cultivation to the Royal Botanic Garden Edinburgh in 1967 but later lost and reintroduced in 1984. It grows easily and flowers well, usually in March or April in Edinburgh, but often suffers from disfigured contorted leaves and flowers if the humidity drops too low. When grown in poor light the flowers can be yellow.

Notes

Named after Pierre Joseph Eyma, 1903–1945, who first collected this species. Eyma was a Dutch botanist who made considerable collections in Indonesia, some of which were lost due to the unrest as a result of war.

Notes

At their extremes the two subspecies are very distinct. However there are intermediates, especially from around Tatsien-lu (Kang-ting Xian). These intermediates include the type of R. bureavioides Balfour f. (Notes R.B.G. Edinb. 13:35,1920) from W China, 1904, Wilson 3954 (holo. K; iso. A), with the large leaves of subsp. prattii but a thicker, more persistent upper layer of leaf indumentum than is usual in subsp. prattii. R. faberi resembles R. bureavii and R. nigroglandulosum in its well-developed calyx and glandular ovary but differs from both in its clearly bistrate leaf indumentum which suggests an affinity with R. rufum.

Notes

Allied to R. kyawi but lacking the setose glands on the young shoots, also closely allied to R. huidongense (q.v.).

The correlation between stout petioles and glandular pedicels, proposed by Tagg to distinguish between R. eriogynum and R. facetum does not hold for specimens now available. The latter name was chosen rather than the former as it already had a wider acceptance.

Rhododendron falconeri subsp. exinuum (Nuttall) Chamberlain

Notes

Closely allied to subsp. falconeri and apparently replacing it in the east. A fruiting specimen (Ludlow &. Sherriff29S9) from S Bhutan could belong to either subspecies. A specimen from the Subansiri district of Arunachal Pradesh, with relatively narrow leaves, c.2.5 x as long as broad, that are glabrous above and only slightly rugose, but with deep rose-pink flowers (Cox & Hutchison 421), may be a hybrid of subsp. eximium.

Rhododendron falconeri subsp. falconeri

Notes

Three specimens from Duke La & Pele La in C Bhutan (Cooper 3911, 3968; Grierson & Long 1085) with pink to lilac flowers, broad, non-rugulose leaves and a fawn lanate sub-cupular indumentum have almost certainly been derived by hybrisation from R. falconeri. To what extent they are part of a stabilised hybrid population is not certain. Their status therefore remains doubtful. It is however noted that a plant assigned to R. falconeri, with yellow flowers and rugose leaves, but with the same sub-cupular indumentum (Ludlow & Sherriff 3041) originated from Chendebi, not far from Pele La.

Nomenclature

Rhododendron fallacinum Sleumer

Shrub or small tree to 6m. Twigs rounded, rough with a dense covering of dark brown scales; internodes 2–10cm. Leaves 3–6 in tight pseudowhorls and with small, slender scale leaves arranged along the stems but these soon falling off. Blade 80–160 x 30–55mm, sub-sessile, ovate, or ovate-elliptic; apex shortly to long acuminate or sub-­caudate, acute; margin irregularly wavy, flat; base rounded to auriculate; densely silvery scaly above, only disappearing gradually; beneath densely overlapping coppery-brown-scaly. Scales variable in size, strongly lobed, the broad margins striate; the centres large and darker especially those of the largest scales. Mid-vein slightly impressed in the proximal ½ above, strongly raised below for most of its length and especially at the base; lateral veins 8–12 per side, wide-spreading, distinctly indicated but not raised or impressed on the upper surface, slightly raised or very obscure on the lower side. Petiole to 4 x 4mm, very short, rarely longer than broad, densely brown-scaly, not or only weakly grooved above in the fresh state. Flower buds broadly ovoid with the bud scales appressed. Bracts densely scaly in a broad central band on the outer side of each bud scale and conspicuously fringed with white hairs on the margins. Bracteoles to 15mm, filiform and papillose below, spathulate and long hairy above. Inflorescence of 15–35 flowers in a complete or sometimes open umbel. Flowers standing erect to horizontal. Pedicels 15–35 x c.1mm, densely brown-scaly. Calyx a low, scaly ring. Corolla 18–25 x 30–37mm, bright orange, without scent; tube 7–12 x 5 x 5mm, densely scaly outside; lobes 16 x 16mm, widely spreading, overlapping to c.halfway and with a triangular area of scales on the outside. Stamens at first standing erect centrally in the mouth of the flower, later reflexing back away from the stigma against the corolla lobes; filaments 12–16mm, slightly broader proximally and hairy in the basal ½; anthers 3–4mm, brown. Ovary 5.5–7 x 1.5–2mm, densely scaly; style 8–12mm, scaly at the base otherwise glabrous; stigma 5-lobed, to 3mm in diameter. Fruit to 35 x 4mm. Seeds 6mm, without tails 0.9mm, the longest tail 3.5mm.

Habitat: Mostly terrestrial, less commonly epiphytic in mossy forest in damp shady places, but also on open exposed ridges, often common.

Notes

Latin – fallax – deceptive or fallacious, because of a deceptive resemblance to R. durionifolium which allowed it to go unrecognised for many years.

It was noted by Sleumer (1966) that ‘sterile specimens [were] hardly distinguishable from those of R. durionifol­ium’. In fact this species is not clearly distinguished from R. durionifolium but is retained here at present. Flower size is extremely variable (see under R. durionifolium) and pedicel length varies enormously as it elongates after the flowers open, even before the corolla has fallen. This leaves only relative scalyness of the corollas and corolla tube length to distinguish between these two species. As conceived here R. fallacinum has flowers with a relatively short and extremely scaly tube, with the scales extending up onto the backs of the lobes, while R. durionifolium

Rhododendron fallacinum has been collected in flower in most months of the year but probably flowers best in the wild from February to April. Pollinators might be expected to be butterflies with the bright display of orange-red flowers with short floral tube and prominently displayed anthers, but Scarlet Sunbirds (Aethopyga mystacalis Temminck) have been seen visiting the flowers. Several hybrids have been recorded with this species in Sabah: x stenophyllum occurs on Mt Alab – it has narrow linear leaves and broad dark scales but has not been seen with flowers; x rugosum occurred on the Mesilau Spur, Kinabalu – it has a mixture of scale types and handsome red flowers; x lamrialianum occurs commonly on Mt Trus Madi and has been seen above the Mesilau Cave – it has intermediate-sized leaves but has not been seen in flower; and x acuminatum, also from the Mesilau Spur, is known only in vegetative form from its intermediate leaves.

Notes

Closely allied to both R. floribundum and R. denudatum but differing from both in its smaller, cucullate-tipped leaves and white flowers, and from R. denudatum (also recorded from lo-chan) in its dense, more persistent leaf indumentum.

Notes

Forms with more or less crenate leaves have been referred to R. cinereoserratum Tan, the type of which has unusually narrow leaves. However, there are specimens with broader but toothed leaves and there are also analagous forms of R. mariesii. We do not therefore consider that there is any justification in maintaining R. cinereoserratum as a distinct taxon.

Notes

R. faucium is closely allied to R. hylaeum but differs in the smaller leaves that taper below, the shorter petioles, and the glandular ovary. The punctate hair-bases on the lower surface of the leaves confirm the affinity with R. hylaeum.

Ludlow, Sherriff & Elliot 13594 & 13620, which differ in their darker pink flowers and more acute leaves, show some of the characters of R. ramsdenianum (subsection Irrorata) but are otherwise closer to the present species.

Notes

The stiff bristles on the underside of the mid-rib and the close network of veins make the leaves of this species readily recognizable. The species is evidently rare. Besides three collections by Cavalerie we have seen only one other (Tsiang 8456).

Notes

Hybrids between R. flammeum and R. canescens have been studied by the present author
at Stone Mountain, Georgia (Kron et al., 1993). This population is most likely the same
as T. G. Harbison's #900 collection noted by Rehder (1921). The hybrids at Stone Mountain are intermediate in flower colour (pink with a yellow blotch on the upper corolla lobe), in floral bud-scale pubescence (the population of the probable R. flammeum parent possesses glabrate bud scales, and those of the probable R. canescens parent possess densely unicellular pubescent bud scales), and in plant height (see Appendix under hybrids of R. canescens).

Although the name Rhododendron speciosum (Willd.) Sweet is often used for the Oconee
azalea, it is not the correct one. Willdenow (1811) cites Michaux's (1803) Azalea
calendulaceo in his description of Azalea speciosa. In doing this Willdenow thus
included the type of a previously validly published name (Azalea calendulacea Michaux)
making Azalea speciosa Willd. superfluous (International Code of Botanical Nomenclature,
1981, Art. 63.2). The correct name for the Oconee azalea is Rhododendron flammeum
(Michaux) Sargent since Sargent (1917) raised Michaux's A. calendulacea vax.flammea to specific rank.

Flowering in April

Rhododendron flammeum, a species that is rather variable in corolla colour and in the pubescence of the floral bud scales, is related to R. prunifolium and R. cumberiandense (see Phylogenetic Analysis). These three red to orange-flowered species are isolated geographically. Rhododendron flammeum can be distinguished from both by its flowering before or with the expansion of the leaves. While it is marginally sympatric with R. calendulaceum, R. flammeum is reproductively isolated from it by the tetraploid condition of R. calendulaceum and the discontinuous distribution of R. flammeum. Although the flower colour is similar between R. calendulaceum and R. flammeum, they can be distinguished from one another by the eglandular corolla tube and the unicellular-ciMate floral bud-scale margins in R. flammeum vs. the densely glandular corolla tube and the glandular floral bud-scale margins in R. calendulaceum.

Flags

Rhododendron fletcheranum Davidian

Very similar to R. valentinianum, differing as follows: leaves with distant scales beneath, the surface conspicuous, green; leaf margin distinctly crenate in the upper half; midrib usually not setose above; ovary conspicuously setose towards the apex, the setae persisting on the capsule.

Habitat: Forests at 4000-4300 m

Distribution: China (SE Xizang)

Illustrations:

Bot. Mag. 176: t. 508 (1966-8)

Notes

Known only from two collections; vicariating with the very similar R. valentinianum

Notes

Plants apparently intermediate between R. floccigerum and R. sperabile var. sperabile occur in SE Xizang (outside the range of var. sperabile) and around Wei-hsi in NW Yunnan. These are characterised by their glandular shoots and narrow leaves, usually with a thick rufous indumentum. Over most of their respective ranges the two taxa remain distinct so the status of these intermediates remains uncertain.

Several fruiting specimens have been tentatively assigned to R. floccigerum but differ in their setulose-glandular petioles and young shoots and in their shorter leaves, 4-6cm long, that are usually glabrous by maturity and sometimes epapillate. In the absence of flowering material their status remains doubtful though they may have affinities with R. neriiflorum rather than with R. floccigerum. They are as follows: Forrest 20305, 20321, 20877, 20855, 22808, 25640,25800,25831.

R. floccigerum is closely allied to R. neriiflorum and R. sperabile but may be recognized from both by its discontinuous floccose leaf indumentum.

Rhododendron forrestii subsp. forrestii

Notes

Plants in which the juvenile state, with leaves purple below, persists to maturity, have been referred to R. forrestii sensu stricto. These may be no more than local ecotypes and are not worthy of formal taxonomic recognition. The more usual form with leaves green below at maturity has been referred to R. forrestii var. repens.

Three plants from S Xizang, Ludlow & Sherriff 1883, 3942, 4751, have the growth form, small leaves, scarlet to crimson flowers and densely tomentose ovaries of subsp. forrestii but differ in their 3-4-flowered inflorescence. The status of these plants is uncertain, particularly as they come from an area outside the range of the species (see Map 121).

Distribution: Indonesia, C Borneo, top of Bukit Raya in the Schwaner Mts

Altitude: 1500-2300m

Notes

Latin – fortunatus – prosperous, lucky or happy; presumably the collector was happy to find such an attractive plant.

This is an interesting species repeatedly collected on Bukit Raya but not yet introduced into cultivation. The flowers are, as far as can be compared from dry specimens, identical with those of R. himantodes but the leaves are markedly different. They are not linear in shape, but elliptic and markedly rugose, with very prominent lateral veins which give R. fortunans a very different appearance to that of R. himantodes. The very wide range of leaf sizes in different specimens of this species is curious and field observations are needed to explain these differences.